Probably because most people don't in their wildest dreams have the kind of spare cash left at the end of the month to do something like this.
Once you have kids to support it gets harder. Not only are there more bills to pay, spending so much time on business means you miss many once in a lifetime opportunities to see the kids as they grow.
The Torah confirms:
"... a man should build a house, plant a vineyard and then marry a wife” (Sotah 44a).
You’ll get all sorts of responses leading the other way:
“no one has money to bootstrap a business!”
Or
“An investor has special capital and asset powers you need it”
Which is nothing but FUD.
Basically, it works if you're building the kind of thing that you can build, and take to market, in 50% of your time with minimal or no assistance. The other 50% of your time will be on business development tasks. Such an approach works when you're a great software developer, and a great businessperson, and disciplined enough to know what you can do as a single person with a small budget.
These are things like small websites, small apps, little doodads that can be manufactured via contracting with someone else and sold on Amazon, ect, ect.
There are plenty of interesting businesses that can be built that way, and plenty of interesting businesses that can't be built that way. (Just try to build something that needs hard capital for tools, like a chip fab!)
- You have a few major clients monopolizing your time, and you can't afford additional resources to break out of the pattern.
- You prove the viability of the product and create a market, but a venture-backed/larger competitor eats your dinner.
I'm not saying it's always correct to accept funding, but it's pragmatic to consider it.
A) They have some ideas they want to launch NOW; not 3-5 year down the road.
B) Saving money won't make a dent in what's needed
C) They don't have access to rich family or friends.
In my local startup scene I've noticed a lot of founders coming from well-paying backgrounds. Ex-Finance, consulting, and such - usually they have pooled money with co-founders from similar industries. Often times in combination with loans or similar from family or friends.
Or even more often than that, you have already successful founders that are spending money from previous sales / exits.
In either case, those tend to be the people with hundreds of thousands to spend.
For regular folks with normal salaries, it's cold-calling every investor under the sun.