Every single person that doesn't ride regularly does. Here in germany that's 99/100 people. If you only do like 100 or 200 km a year you hardly ever get a flat so people don't even think about being prepared for that. Thus they don't know that a tube and some tyre leavers maybe 10€ online and that includes shipping.
Fixing everything yourself is much cheaper in the long run and more importantly it's usually faster too. There are hardly any bike shops in my area that have road bike consumerables or any road bike parts in general. They are set on hybrid / some MTB and well 99% ebike stuff these days so they'd have to order whatever part I need, install it (which takes a long time because they have a billion ebikes to do maint. on 24/7) and then I have to pay 3-5 times the price of the item and necessary tools. Fuck that
Everything on a bike is super easy to install, fix, replace and set up. There are tutorials for everything and they are usually less than 5 minutes long. Only wheel building is a bit more tricky since it requires some decent and rather expensive (compaired to the usual bike tools) tools if you want to do it well.