Peg-in tx’s have to allot enough time because you could be pegging in from a coinbase tx and those need 100 blocks to mature.

https://bitcoin.stackexchange.com/questions/22548/coinbase-maturity-of-100-transactions

Then add 2 more tx’s for Liquid sidechain finality.

I think most people will never appreciate how much thinking and design went into Liquid to make it very secure and resilient. There are so many cryptographic edge cases to deal with as well.