Ohtani is forced to sign a minor league contract due to the collective bargaining agreement. Teams are limited in their offers. The 3 teams who can offer the most happen to be AL teams (Rangers $3.5 mil, Mariners $1.5 mil, Angels $1.3 mil). Offers from the NL (Cubs, Dodgers, Giants, Padres) are restricted to $300k offers.
Unfortunately that is a large pay gap to choose a league based on a DH rule.
Yes, but if he truly cared about the money, supposedly he could have waited a bit longer and done much better. It's almost a freebie for those teams (aside from the $20 million posting fee), given the salaries for top players these days.
If staying in NPB, Ohtani would have 5 more years left on his Hokkaido contract where he would be left to renegotiate. Rather than keep him, his Hokkaido club decided to get the full $20 mill by posting him this year, cashing in on his recent numbers. Ohtani is potentially better off signing the minor league contract and quickly earning an mlb contract rather than being stuck in the 5 year NPB contract.
Five years is a long time, agreed.