The 3 highest scoring teams are on pace for 1,964 IP, 1,907 IP and 1,751 IP respectively.
Right now the same 3 teams have 14, 17 (4 are on the DL) and 10 SPs respectively.
There is also another team on pace for over 1600 IP and that team is already playing for next year.
I think the answer to your question is that they realized earlier that with no IP cap, you could get an advantage if you could max out your SP starts each week at 14. It also protected them against “losing” a start when more than 2 SPs were scheduled to pitch on the same day. That would still occur but they would have enough other pitchers to fill in the other days to make sure you got 2 SP starts every day (or as close to as every day as possible).
Keeping the 1500 IP cap would seem to solve this problem. Teams would have to watch their cap and make sure they paced themselves out correctly.
Also, opening up more SP slots would also help because it would lessen the incentive to stockpile SPs beyond normal depth. If you’re able to start your top 5-6 SPs every week regardless of what day they pitch on, it creates less need to have extra SPs on the roster to make up for the lost starts when more than 2 SPs are pitching on the same day.
Kudos to the owners of those 3 teams for recognizing the benefit earlier, but it is resulting in every other position losing value compared to SPs except on the odd week when two of these 3 teams are playing each other.