Why is living with your parents considered a bad thing?

I'd be really curious to know what happens to you between your early 20s and your late 30s

As some people said in this thread, it's hard to get a job that pays well out of college. You're supposed to be using the help of living at home to work towards getting an actual career so that you can afford to move out by/around 30. If you are in a difficult financial situation in your 20s and you instead spend them spending your money freely and frivolously without bettering yourself, you'd be rightfully seen as "lazy".

I graduated with a degree that didn't work out in the path I originally saw for myself. I moved back in with my parents at age 22, and spent my 20s:

1. Working whatever desk job I could
2. Saving as much as possible
3. Teaching myself programming at night

I would not have had been able to do the 2nd and 3rd things unless I was living at home, because I'd be putting all my small pay towards rent and living expenses, and also probably be too tired to learn a new career as 1 entry level job is not enough and I'd probably be working more hours or a 2nd job to make ends meet. At the same time, if I was not doing those things while at home, I'm wasting an opportunity and my privileged position (not everyone can move back), and would see myself as lazy. In my 30s, I have an actual career and had put myself in a good financial situation thanks to that opportunity of being able to move back in.

I’d be really curious to know what happens to you between your early 20s and your late 30s

You're supposed to grow up and become independent.