The reason they disbanded is because they aren't that talented.
They got lucky because big corporations are run by idiots who don't know what security is. Lulzsec would never have been relevant if it wasn't for the fact that Sony didn't implement basic SQL injection protection (mysql_real_escape_string would've prevented this whole thing from happening).
They soon found out that other big companies have half a brain. So they unsuccessfully tried DDOSing with a botnet that was way too small to do anything serious (probably not even their own botnet). After that they realized they better quit before everybody realized that they aren't skilled enough to stay relevant.
Any decent coder who had any amount of free time on their hands (aka unemployed, or under 21) could have easily done everything that LulzSec did. That's why (even though I support most of these people's actions), everybody who is getting caught is a broke loner. Meanwhile all the hackers who actually know what they're doing are quietly making tons of money.