For some, but for many it’s the confidence and the belief that they lack the tools and skill.
I had a Dutch girlfriend in London who grew up riding a bike to and from school and to her horse every day. One of the vintage classic bikes I bought was for her. Her Dad used to maintain her bike for her as a kid and teenager, and so she never learned how to maintain it. And she did want to learn how to maintain it. She was eager to learn how to fix her bike and signed up for a course.
Both of my sons live in London and commute daily to and from work by bike. It’s quicker and cheaper than public transport, and they get some exercise. One has a folding electric bike and the other has a classic vintage bike, and everything vintage is considered cool in London these days.
On the other hand, the explosion in cheap rental bikes has imploded the bike market for sales for most bike brands, and the whole bike industry is struggling with profitability at present.
In bigger cities if you want to learn to maintain your bike there are small clubs which have all the tools you need and can drop in and get help if needed.
I recently spent a year in La Rochelle and there was a similar club there “
Vive le Vélo” where I bought a second hand classic road bike and a few evenings a week you could drop in and use their tools and get help if needed to maintain your bike.