Adobe is not doing any new development for CS5 or CS5.5 or CS6... everything new now is for CS7, aka CC "the Cloud"
Since CS5.5 is now "old" software, I doubt that anyone is doing anything new for that version... just a fact of computer life
I feel your pain.
It's a lesson you learn at some point, although a sour one. I remember spending thousands of euros on studio licenses of Maxon Cinema4d 7, 8 and 8.5, and with version 9 the upkeep became so high I figured I would update one version later - only to find out my license was worth even less, and the upgrade costs would have cost me an arm and a leg. At that point I cut my losses, and switched to Lightwave and Blender.
Same with Adobe: I refuse to buy into the CC subscription, and I had to swallow a couple of times realizing all the money I invested in Adobe software over the years would become yet another lost investment (well, to be honest I did make good money over the years using Adobe software, fair is fair). Let's say I lost my time and skills investment. Anyway, I switched to other software almost two years ago now. I do still use Adobe software in my instructor career, but not for my personal and professional work.
Nowadays I try to stick to and support open source as much as I can, and I support the smaller indpendent developers. I have not regretted this decision so far, quite the opposite. Large behemoths of companies only care about shareholders generally, and less about their loyal customers.
Not bad or good, merely reality. If you do not like the current situation, change your situation, and take control. Or be happy with what you have - this society and its companies unfortunately continuously endeavour to keep people unhappy and cause endless consumerism - in the end it is not Adobe making us unhappy, it is ourselves who make us unhappy by always wanting the newest thing and comparing ourselves to others.
Yeah, capitalism sucks at times