The purpose of deflation tokens is to create scarcity for the token and maintain value for the project. Such projects are usually DEFI projects.
The above projects are getting more and more frequent because duplication of the source code of previous projects occurs more often. Projects that survive and increase their value are projects of quality, continuous innovation, and strong communities.
I think you are mixing deflationary with DEFI, they both AFAIK are different things. They are relatively new to the market and aim of deflationary coin is solely to decrease the supply to coins with time. Lets see what impact they made in coming days. Wake me up for there next bull run.