It actually doesn't. MDK, Lexe, LN, Spark, Ark, e-cash, etc. doesn't support it. Few wallets support it. Basically no one could test your apps. The goal here is to make it easy for people to test and rapid iteration.
I'm not entirely sure that it is true for everything you name there but no point in arguing. I'll put up some more infra for testnet, and make this constraint go away.
It actually doesn't. MDK, Lexe, LN, Spark, Ark, e-cash, etc. doesn't support it. Few wallets support it. Basically no one could test your apps. The goal here is to make it easy for people to test and rapid iteration.