There have always been pitchers who can hit and hitters who can pitch. I think Rosco is right, it is mostly to do with coaches and management thinking (perhaps correctly) that it is better to have an excellent hitter or an excellent pitcher than one who is merely good at both.
I think another factor is that good pitchers are so important that if you show any potential to be a good pitcher they really want you to focus on that unless your hitting is truly exceptional and your pitching is marginal.
Ohtani is special because he is excellent at both. That is extremely rare.
I too usually view the two-way players not as future Ohtanis, but as guys who have twice the possibility of becoming useful contributors. I now have 10 to maybe 20 of these in my system. They require MUCH more work to develop than regular players.
RL baseball managers know much more than I do about these things, so I won't discount their judgment on not developing two-ways. But I will say that having a two-way player in OOTP is extremely useful. Until he started to not really be worth his cost, I used Lorenzen quite a bit. Effectively having an extra arm or an extra pinch hitter is very handy. I could also do things like warming him up when I knew the pitcher slot was up, letting him hit and then pitch, or vice-versa, saving use of a player.
I even had one guy my first year who was mostly a power hitter but could pitch on occasion. He threw mop-up for me and could at least keep the game closer than a position player getting smacked around.
All that said, someone who excels at one thing is still usually better than someone who is merely decent at two, a lesson I learned the hard way in my first amateur draft.
Here's my personal "Ohtani Junior" freshly promoted from the IC. I am sure he won't become nearly as good as this, but it's fun to dream.
PS The Game, right-click any player and select "Set Game Strategy" and you'll see "Use as a two-way player" bottom right.
