IMO, this comes from the fact the feature was designed with a very narrow use-case in mind. MAST was just about pushing more unlikely spending conditions more down the tree. Luckily this can still be used in a different way (and 128 is then just some arbitrary limit).

A good reminder that when designing an API we shoud give the consumers some lego bricks and then allow them to come up with something creative on their side instead of prescribing what exacty can be done and just giving them a few very rigid methods.