It can be picked up rather easily in a modern car, sure, but I'd like to note that not all manual transmissions are the same. As in, to drive many of them well, it does take a patient instructor and diligent student to understand the fundamentals, timing, muscle coordination, etc. To your point, yes, everybody can probably do it, but can they do it well?

The test I grew up with was a 1991 Ford Ranger, V6, 5 speed manual. The clutch engagement was extremely narrow and the V6 was kind of underpowered, especially with the A/C on in Texas, so learning how to make smooth take-offs was very difficult. I wasn't allowed to take that truck out on my own until I could drive around a passenger with a cup of coffee, not to the brim but definitely there, and not be rough to cause a spill. It was a high bar in my opinion.

Years later, my VW GTi 5 speed and clutch felt like an absolute dream, buttery, easy. Learning on the much harder transmission, in my opinion, was beneficial.