Never let your team BM

Video link: https://youtu.be/mO9bVqPR678

I am the Irelia in this game. We had just won a teamfight in their base and it was an easy push to the nexus. After the first turret went down, I kept trying to push to end the game and literally the rest of my team stopped attacking and started bm'ing (@0:44). This resulted in them all dying while I keep trying to destroy the nexus. After Lucian falls, I try to kill MF because I know I can't end if she's dps'ing me, but I end up dying to the fountain (accidentally) the very end. We ended up losing this game. Is this intentional feeding/griefing on their part? Thanks. And to top it all off, this was during my plat 2 promos..