Well there have been numerous tries iirc, but they all boiled down to how BF2 uses it's networkable objects and how the engine uses the RAM on a PC.
The devs have done a lot of things to improve the performance (better shaders, better resource loading, etc...) while pushing the engine to it's limits, but here's the crux. FH2 looks on par with games from 2010 on an engine that was made in 2005 and thus has mutated to the best hardware benchmark program you can wish for. If there is one single error in your RAM, then it will CTD once it touches that on bit in your RAM address. ^^
A solution would be to reduce the number of vehicles, statics and kits on a map, but that would really be a pitty imho.
Just load back up once you CTD! With modern hardware that takes less than 2min.
I seem to belong to the lucky few who can play 3h without a CTD, but that's how I'd do it if I'd ctd.