BYU joins Big 12 (2023-2024)

BYU along with non gymnastics universities Cincinnati, Houston, and Central Florida will join the Big 12 after Oklahoma and Texas announced they were leaving for the SEC.

Big 12 is back to 4 teams. However, that leaves the MRGC with just 3 teams, Boise State, Utah State, and Southern Utah. It will be interesting to see if these 3 will remain a conference or perhaps all 3 would join Big 12 as affiliate members for gymnastics only making the Big 12 a 7 member conference.
A third option is these teams could join Alaska, Air Force, UC Davis, Sacramento State, and San Jose State in the MPSF making an 8 member conference.

Why are these conference moves always announced so far in advance? I mean I understand needing a year or so lead time, but 2-5 years? That seems odd. Is it television contracts?

Usually conference championships are assigned a few years in advance, it gives enough time for the conference to realign if need be, and as you mentioned television contracts, etc. At least for the big 5 conferences: SEC, PAC 12, BIG TEN, ACC, BIG 12