First mover advantage, brand awareness, word of mouth, early reviewers, etc. People then build a brand connection of "robot vacuum" == "roomba", everything else is just a fake imitation.
Imagine you're a normal random consumer and not an electronics nerd. You've heard people on the morning TV news show talk about these robot vacuums and showed a Roomba. You have a friend that got one last Christmas and said their Roomba was pretty cool. You go to the store, and you see a few Roombas and some other brands you've never heard of. You're probably only going to spend a few minutes looking at the shelf. Which one are you likely to get?
And in the end iRobot managed to coast on that brand connection of "robot vacuum" == "roomba" for a lot of people for nearly 20 years. It really only took until competitors were way cheaper and way better that got people to really start to switch. Their products have not been competitive for over a decade and yet they've only finally died. That power of linking a brand to a specific item or service is powerful, and its not purely push advertising and forced video ads that build it.
Its somewhat the same thing for Google. Sure, they do some amount of advertising especially at top of line events, but overall it seems their direct outbound marketing is kind of low overall. They spend a bunch of defaults and continue to build the connection that to search the internet is to Google, even as they continue to inject more paid results and the quality declines. Other competitors are out there which are comparable or better, but even with them heavily advertising they fail to unseat that brand connection.