Stop Playing in the Jungle

A lot of games recently I noticed a trend; laning phase going as usual, first tower goes, roaming happens, etc. You notice a pattern from the enemy team, they're always grouped up, almost all 5 all the time. So you try to rally your team together. Only... the fucking jungler is farming crows. Team fight midlane, tower going down, multiple pings for back up aaaand... they're still farming wolves. This is on top of the fact that they've been absent from any lane ganks, and haven't gotten or assisted in any objectives.

Is there a strategy I'm missing here? If it's glaringly obvious I'm sorry, but at 35min in, farming some golemns during a team fight or dragon takedown is not going to do much to help our win. It's getting increasingly frustrating and I'm starting to wonder if there's just something obvious that I'm missing. Yeah I know a little gold perk, some extra XP--but does that really outweigh the cost of a team fight and losing a tower or inhib? Please, let me know if I'm out of line. Seriously, I'm no pro, but this is something I've noticed in almost everyone one of my games recently.