Bip300 is a lifeboat for bitcoin. Its insurance against a future tech that might threaten bitcoin.

If drivechain had been implemented, the blocksize wars would not have happened.

All politics move to layer two, where consumers can choose what features they want. Other L2 solutions have negative tradeoff such as custody.

Bip300 swallows them all, not to put them ON bitcoin, but next to it, with no threat to bitcoin-main.

There are many other good reasons.