I've effectively "fixed" a couple startups built by fresh college grads and interns and made a pretty penny doing it.
I think some companies and some founders have thought engineering was an area where they could cut corners by not hiring experienced people, and they have learned this is a good way to fail.
That being said, you want a mix - more seasoned people leading the direction, processes, and technology selection; and younger people for their energy, enthusiasm, and willingness to learn new things.
This is actually an example of age discrimination. Young people can be in leadership too. I always see conversations about ageism in tech drift towards older workers but as someone who was precocious I was often denied opportunities I was ready for because I didn’t have “enough experience”.
The central theme of anti-discrimination is not judging people for things out of their control (age, gender, race, somehow religion gets in this category too, etc.) and instead being free to judge them for any of the things that they do control.
Experience is a weird one in that it's what they've chosen to do (ok to use) but wanting to see more experience will either mean they had more time to do things (not ok to use) or didn't waste so much of the time they had (ok on the surface, but you'd need to know the person's age to calculate whether or not the amount of experience you desire was within the range of possibility for them).
I should add generally here - you'll have younger people who exceed their years and older people with more enthusiasm and energy than the former.
Experience is really about making mistakes and learning from them and that takes time - there's really no substitute. People who are ahead of their years usually started earlier and worked harder at it.
So the problems I see are a team that's all one or the other and generally that's not good -- it's impossible to find a group of 10 new-grad engineers who all over-perform their age by 10 years.
I think some companies and some founders have thought engineering was an area where they could cut corners by not hiring experienced people, and they have learned this is a good way to fail.
That being said, you want a mix - more seasoned people leading the direction, processes, and technology selection; and younger people for their energy, enthusiasm, and willingness to learn new things.