They keep coming back on the market because for DEVS, creating such kind of project is easy money.  Most of the project that produces high inflation emission often use it to bait investors into investing in their project telling them that their investment of x money that will receive y amount of token can emit or produce a profit by thousands of percent in a short span of time.

People will never learn and those who profited in this kind of scheme will always jump into it even though the succeeding investment will be losses.