What banks do not use Zelle?

I'm curious to know which banks do not utilize the popular peer-to-peer payment platform, Zelle? Are there any major financial institutions that have opted not to integrate this service into their offerings, and if so, what are the reasons behind their decision? It would be insightful to understand the potential drawbacks or limitations that may have influenced their choice not to adopt Zelle, and how this impacts their customers' ability to make quick and convenient payments.