It wasn't because the PS3 is really good at security, (See: Pexploit + PSNStuff (Yutolio's Database) + TrueAncestor BACKUP Injector 1.50 in all OFW's up to 4.70), but that's only a hack that allows you to play certain PSN games, and older things (Like, Crash Bandicoot or FFVII on the PS3 without using the PSN store) but there wasn't specifically, a support for the console after 3.55, want to know why?, easy, because each FW is a huge mess, Sony purposefully managed to make each FW with their own code, their own features, etc.
It doesn't protect automatically or erase things from older firmwares, Sony decided to just make every FW after said version mentioned much more complex than any other one, and also making each new one different than the last one, as a response after Geohot could "link and chain" several CFW's in each FW of the PS3, take into other fact that the PS3 has a complex architecture, with several load checkings and you have a console that no one would bother to hack until, idk, Sony decides to stop supporting for the console, since what happened to GeoHot.
The only user (as far as i know) who is bothering to even try in doing something, is modrobert, with his investigation regarding the PS3 XDRAM Serial, he managed to conclude the experiments only 11 days ago, and while we could potentially write something onto the XDR DRAM using the serial DRW Command (For more information check the Elpida_E1033E40_EOL_0.pdf attached to a post in the forum he is working to) the thing is, everything has to be wrote on the Memory Interface Controller, which we don't have control yet until someone manages to control the memory bus of the console, and even if someone manages to do that, then the serial Interface becomes useless.
The scene has been going for quite a while, but the most progress that has been made it's indisputably by Nintendo consoles, the DS got hacked fairly quickly, the 3DS got also hacked after two years with the Gateway 3DS, the Wii U got hacked, and is still in development for a future IOSU exploit, all of this makes Nintendo the easy target for hackers in general, Sony and Microsoft are two different beasts however, the first had the PSP, which is a system that basically came pre-hacked, PS1 and PS2 consoles are also fairly easy to hack, however, the PS3, PS4 and Vita did plenty of changes compared to those consoles.
The main change is, that the PS3 had different versions of firmwares on each console, making it impossible to hack unless you know everything about the console, and the possible changes it may have, the PS4 is more or less the same thing, it got the Brazilian/Russian method of hacking though, but still has a long way for a CFW to be made right now, the best thing we can all do is wait, i hope that eventually, the PS3 gets hacked by the next year, if it ever comes the case.
So TL;DR the PS3 is a complex console to hack right now.