For me, it's because, even at first level, Bards are adequate at support. Bardic inspiration, particularly, is amazing at 1st level - when your proficiency modifier +2 getting and avg of +3 to a roll is pretty big. Sure it's a long rest resource, but the Bard will likely be able to do it around 3 times per long rest - as many as the lucky feat.
And yes the Bard gets relatively few spells, but they're a good selection. Sleep is practically instakill at 1st level, Faerie fire is also quite good support. As for cantrips, viscous mockery may not be damaging - but it's excellent support.
Also, at first level the bard is almost certainly going to be the best at social interaction.
IMO they have too much going for them to be near the bottom here.