I see now, the same thing is happening for me. It's happening for both Subject Tables and Detailed Tables. It seems the issue has something to do with selecting "All ZCTAs in United States" or for a given state; if you select a specific ZCTA, then other years are visible. Maybe someone here from Census can look into it.
In the meantime, I can suggest a few other options:
1. Download the full summary files for each year (you probably don't want to do this; it would be a big project).
2. Use a third party tool, a variety of which plenty of people here will be excited to recommend. (I'm a PolicyMap partisan, but you'll need access through your university, and it doesn't have overlapping years of 5-year estimates; eg. only 2015-2019, 2010-2014, and 2005-2009... but that's because you shouldn't compare overlapping 5-year estimates, like 2012-2016 and 2015-2019. Census Reporter might also be a good option.)