As a university professor, I still get random people e-mailing me “dumb questions” every once in a while. And I still try my best to answer them – in the spirit of keep the Internet alive!

Online community and connections are very valuable, and I also get genuinely interesting e-mails from random people. Usually someone who has read something I wrote, and want to discuss it. I also send out random e-mails, and my experience is that many people will answer, if you write to them about something they care about.

I respectfully respect the premise that the choices are "paper books" or "Youtube influencers", though I'll note we didn't have Gilbert Strang's 18.06 course back in 1999 either.

I'd also note that the Internet of 1999 was loaded with spam, bursting at the seams with it, so much so that it was actually a big deal when ~30 months later Paul Graham wrote a post about Bayesian filtering.

you still can (at least, professors. not so sure about industry experts). I've done it on a number of occasions

You can still email people! A genuinely interesting email will probably get at least a 20% success rate