Without the play offs, the season would just "fizzle out"..
The "winners" of a league that has no real financial reward, nor any publicity outside its own bubble, will make their money (hopefully), by running a semi and a final that attracts maybe a couple of thousand more combined than they would have got for two "run of the mill" meetings at the end of the season...
Sheffield won the league (or was it Leicester?), but I would say that more attended their play off than would have attended their league winning meeting (in fact I don't think they even had one as Leicester losing gave them top spot didn't it?) .
The Aces were pretty much guaranteed a play off place and, around the SON time, their crowds dipped noticeably, (probably due to the cost of the SON tickets), therefore the play offs brought in much needed revenue...
Not many speedway meetings (in the UK), look as if they "mean something" therefore the play offs at least give the sport some kind of purpose, and drama...