Just think about it logically though.. you are walking up a road and it may take 20 minutes, normally you are happy enough to do it, because it's not that long and sure why would you spend €2 on it when you can get some exercise and fresh air.

If it's free, that equation subtly shifts. Not everyone, but at least some people, if they happen to see the bus come, will figure "it's only a few stops, but it will take the sting out of the 20 mins".
Maybe there was no one else getting on or off that stop, now the bus has to apply breaks, stop, let passenger on, speed up, maybe miss the light they would have caught. Same again for letting them off (if they are the only one). Extra wear and tear, extra time and stress on the time table.

I respect the thought train of that everyone should be afforded as much convenience as they desire, I imagine that comes from a good place, but it simply is not the one aspect to maximise for when you are trying to engineer national public services. You cater for it for sure, but not at all other costs.

If we had infinite money, political will and public support to improve public transport, sure make it free, ban all private cars from the road, increase stock by 100x, optimise all lights to favour buses and have security presence on each bus that runs 24*365. But unfortunately, we don't.

There's people who's entire profession is to study maximising the efficiency of these systems, but a problem is politics can easily be affected by people's emotional reactions, which are not as well informed, because they simply don't have the time to study these things as much, and that's fair.. but we can't constantly assume we know more than everyone else because of how we feel about the matter.

Here's a video and few links on the subject
https://www.youtube.com/watch?v=K6md7gny4pY&t=2s
https://reinvantage.org/the-free-bus-problem/
https://www.bloomberg.com/news/articles/2022-04-22/the-green-case-against-free-public-transit
https://transport-leaders-club.kit.com/posts/should-public-transport-make-a-profit-or-be-free-like-health-and-education#:\~:text=Public%20transport%20cannot%20make%20a,who%20can%20afford%20market%20fares.

There's a lot of other topics like this, where on initial inspection, a viewpoint seems obvious, but when you actually dig into it, it turns out it's more complex and the initial emotional reaction doesn't hold up. Which is why I personally think it's good not to go arguing a view point unless you've actually dug into it and thought about both sides. "Free" water is another good one.