Because it is based on different technology.
Vision runs on the client PC.
Perspective runs on the gateway and the client is a web browser. There are all sorts of technical issues that have to be addressed for this reason, including security and reliability.
The momentary button question has been discussed many times on the forum and good reasons given why you shouldn't attempt it with Perspective. Here's one: How to create the momentary Button in Perspective - #7 by pturmel.