What reason is there to not admit Stanford if they're willing to drop revenue sharing requirements? Absolute no-brainer.
for the ACC, there would be a few issues. First, just Stanford would cause an unbalanced number of teams. And that would create even bigger issues for non-football, in that ACC teams wouldn't have another CA/West Coast team to play on a weekend out West. Second, the ACC's TV contract isn't competitive, and it's not up for renegotiation until 2036. So unless Stanford would agree to no ACC TV revenue until the next contract (i.e., over a decade, which seems unlikely they'd agree to), then at some point when they receive funds, then the existing ACC schools would be getting even less $$ from a contract that already has them earning much less than the B1G and SEC teams.
for the B1G, they already have 4 West Coast teams. I don't think they'd want an odd number of such teams. The B1G's TV contract doesn't last as long as the ACC's (I think it's up in 2029; not certain), so if they could get The Cardinal to agree to no TV revenue until then, it should at least get them into discussions. Beyond that, I think it's a question of what the B1G wants IF it does expand. I think their preference would still be Notre Dame plus 1 other school (I have no inside info; just speculating as well as reading everything I've linked). ND & Stanford might work (even though it still leaves an odd number of West Coast teams), but I just don't see ND making a move unless their TV contract negotiations go nowhere. While poor TV contract negotiations may happen, I don't think that will be finalized in the coming month, which means the timing isn't great for Stanford. The odd number of WC teams could be resolved with Cal, but that likely makes it final that ND will never be a part of the B1G, which may be tough for some of the B1G execs to stomach. Plus, the B1G has done extensive analysis of the Pac teams, and didn't invite Stanford & Cal when they added Washington & Oregon, which should indicate something.