I think a reason some people don't create there own is because presently there's often so many up.
If I look through party finder and see 15-20 Zurvan Ex farm parties all with 4-5 members. but no space for tanks or heals, the only jobs I have above 260+ (see below) I'm not going to create yet another farm party.
My biggest issues with party finder though are:-
1:- I level requirements. Party leaders should not be allowed to set an ilevel higher than there own. I Joined a zurvan farm yesterday with an ilevel requirement of 262 only to find upon entering the fight someone pointed out the leader and his friend were barely i250. Not even meeting the entry requirements for his own party. Group was useless anyway the leader and another kept screwing up cross and telling the 6 people that were all perfectly stacked they were in the wrong place... 2 runs and most people bailed including me.
2:- The other issue I have is people labelling things "clear parties" when they clearly aren't. I join a few of those time to time. Help out get some lights /second chance points /maybe even a bird. Only to find many of these parties are a very long way from clearing the fight.
Did a Seph ex one yesterday as paladin. At one point I even had macros. For stack in B. Spread for da'at yada yada. and people still couldn't do it. I would hit the stack in b macro as soon as the third tower came up. And find I'd be able to run to my tower. Wait for it to dissappear and run to b to bait pillars before the blue circles started appearring and I'd still be standing in b 3 or 4 seconds before anyone else even started to move to b. Only to then watch the flash and pillars kill everyone..
Seriously they probably had at least 10 seconds notice that they needed to stack and where and they still failed. "Yeah this ain't a clear party " and I bailed
Then I did a sophi clear party on ninja and laughed first run both healers knocked off by the first gnosis. Second run laughed so hard when 5 ppl got punted off by the first deemerge. "Yeah this is not a clear party at all" and again I bailed.