I was doing this too! But as a true millennial I had two complaints:

1. I still had to load the photo app when I approached the gym, which annoyed me. The lat/long encoded in the mobile pass just has it pop up when I'm nearby.

2. I wanted to be able to leave my phone at home and just use my apple watch.

Additionally, the code never changes so you never have to update the mobile pass or visit my dumb website again.