I'm gonna pull a random theory out of my ass so stay with me here. MLB The Show first appeared on Xbox in 2021, and is published by MLB. The Switch variant then appeared a year later. This was after the renegotiation of SIE and MLBs contract in 2019. As a result, MLB has been publishing the Xbox and Switch variants. During this time, SIE has not only developed and pushed their live service initiative, but also multi-platform. Their live service games have day 1 PC releases and there have been job postings related to mobile development from San Diego studio for years. So why no PC or Mobile variant of the game yet?
What if the contract from 2019 had a time period set to it? Maybe 5 years worth of releases for example and then the publishing rights revert back to SIE? Well, 2025 would have been the 5th year of published releases, so maybe 2026 we see Sony acquire the publishing rights for Xbox and Switch, and also the release the mobile and PC variants so they have full publishing control across all platforms?
Again, random ass-pulled speculation but figured I'd toss it out there.