I don't know about bugfixes in particular but CurseForge indicates that they are still being updated and even new mods are still being released:
https://www.curseforge.com/minecraft/mc-mods?filter-game-version=2020709689:4449&filter-sort=2 ("sort by" at the top of the list includes most popular, last updated, created, name , downloads)
In fact, mods (other than my own) are still being updated and even created for 1.6.4 and even older versions:
This page includes mods for Beta 1.7.3 which were created this year, some updated this month (presumably under 1.0.0 since CurseForge doesn't include Beta versions, Beta mods might also be listed under a release of the same version number, e.g. 1.8 for Beta 1.8):
Of course, most modders update to newer versions and much like Mojang, do not release updates or bugfixes for older versions.
Yah ik, also curse can be quite confusing when browsing a mod and you'll have show all files to see updates for older mc versions
but take mekaism or applied energistics as example, both mods decide to switch to a newer mc version at some point and older mc versions wont get fixes that are done in the newer versions
i guess it's just to much work