Will they use it again next year?
Almost certainly not, but I've had bees swarm into a particular hedge two years on the trot so anythings possible.
If you've had that many swarms available to collect you really should have tried to get a hive to put them into, the cost of bees next year will be say, £125 so it would have paid you to collect them and home them while you had the chance. Had nobody got any second hand stuff you could have got your hands on?
Also has nobody else collected these swarms, have they just flown off, if so they've probably been lost altogether which is a great shame considering we're so short of bees.
Why so many swarms?
Well it's just been one of those years, the rain keeps them in, they get bored and make a new Queen, first bit of fine weather and they're off. That's my take on it anyway.