- Numbers advantages. If you're too weak to 1v1 and too weak to 2v2, then 3v1 and 4v2.
Lots of people get into the mindset of "I'm behind. I need to farm and catch up." Then they simply get picked off while solo farming, and the game falls even further out of control. If your team is behind, it's okay to have a member solo farming/splitpushing, but you generally want the rest of the team roaming as a gank unit to try to find picks. If you have five weak players moving as solitary units trying to farm, you're in for a really bad time.
- "I often find it difficult to farm when the enemy flanks me when I am farming towards their turret."
Then don't farm there. Just like you said, "I cant split push since the enemy team pushes our lanes making it harder to get turrets." When a team is ahead, they tend to shove up the lanes very hard. Even if they aren't looking to create wave pressure, they do it indirectly because people in solo queue always want to farm the side lanes before grouping. That means the creeps are going to push to your towers, where you can CS more safely. Why run all the way up to river to CS when you can hang back and get them at your tower 10 seconds later?