The buses are physical symbols of privilege to these protestors and they are accessible. It's not hard to figure out why they have become the focus.
Let's be honest the only meaningful public spaces we have in cities are roads and sidewalks, probably 80% of public space. Roads and parking lots together are probably 25+ percent of many cities except New York. Those spaces are as big as they are because of cars. If we didn't have cars, the overwhelming majority of roads would not have to ever have more than one lane in each direction.
Does Google supply their people with cars? Do cars use the city bus stops? Most people do not share your "no greater symbol of frivolity and privilege than owning and driving a car in the city" view. Cars are still part of the US's culture.
A private bus that uses city stops is seen as a much bigger symbol of privilege than any car. It is a single focus point and can be spun into the "let them eat cake" vibe a protest like this is looking for.
If you own a car in Raleigh, NC or Austin, TX for example, it's part and parcel of living in urban sprawl. The trade off is lower housing costs for greater transportation costs. If you live in NYC and San Francisco, a car is optional unless you make a living in a job that requires frequent daily travel. For everyone else living in a dense urban area it's a luxury that comes at the cost of everyone else since cars compete directly with buses for the use of the commons (roads).
I used to live in São Paulo, Brazil, and besides maybe Beijing, PRC (where I also once lived), there is nothing more damaging to the public good than all the people with the money to own and operate private vehicles in a sufficiently populated area that can't really afford having everyone own a car. São Paulo has about 5 million cars in a city of about 20 million. The cars directly compete with buses on the roads and every car hurts the average bus user. Every person who gets sick of buses and buys a cars is screwing over all the people they once shared the bus with making it a little bit worse so that the threshold for getting a car is crossed for a few more people, perpetuating a vicious cycle. There are days when it rains in São Paulo, where the traffic is so bad that it takes 3-4 hours to cross the city in a car. In a bus? I can't even imagine that hellish experience.
On the 7th of September for example, 3 million cars will leave the city over the course of like 48 hours, clogging up every major road for hours. I used to go to a place called Maresias on the coast, which is 2.5 hours by car and 4 hours by bus normally without traffic. With traffic it can get as bad as 4-10 hours by car and 6-12 hours by bus.
There simply is no mode of transportation more selfish than the car and it is only second in level of privilege to transportation by helicopter.
The retort from some single mother of two who has a car because she needs to drop her children at daycare (not on bus line) and then drive to work because "common" people don't have onsite daycare or fancy buses right to the door will be amusing. I will bet the reporter could even find a more sympathetic story. Bonus if the single mother needed to move farther away from her job because of higher rent.
If you think the above is silly and off topic then you are missing the attack vector. Welcome to modern attack politics.
Why the buses are the symbols and not the limousines or private planes that executives take to work; and are probably also provided by their respective companies.
It's so strange to me that in this situation the "haves" are such (relative to the aforementioned executives) modestly compensated tech workers.
Those aren't trappings of the people displacing the people in the neighborhood. Look at the actual income stats in the US and you will see the "modestly compensated tech workers" are actually in the 90+% of income earners. $120,000 is 97%, $150,000 is 98%. These are the "haves".
And yes I know that a six-figure income probably places you in the 90%.
However these people aren't the decision makers and can't affect change the way Google's or Apple's executives can. Until the protesters start protesting rational targets it's hard for me to commiserate or take this seriously. (clarification: I absolutely commiserate with people "gentrified" out of their neighborhoods, I just think the protesting has been directed at the wrong things)
So many of the articles include a quote from a protester that the "techies" don't interact or integrate with their neighborhoods. But I've also read many quotes from techies stating that they are unhappy with the situation too, no one wants to displace people from their homes or neighborhoods and high real estate prices hurt everyone.
If I were involved in one of these protest groups I would take the first step, get the employees involved too, and make it about something bigger than these red-herring buses!
Why? The tactic they are using has worked countless times. It is a tried an true game plan. Keep it simple and demonize all of them. The workers are better defined as part of the problem and, yes, 6 figures means you are the "haves". Those workers are renting in the area and seen as kicking out the normal folks.
The reporter writing the articles will be sympathetic as his/her career has probably felt the same pressure from tech. It might be a nice analogy for one of them to use (tech: residents -> force out of homes, reporters -> force out of careers).