[Official Site] TICKETS | PLYMOUTH ARGYLE (A)

Quite a few reasons.
Some Independents have very few, if any, overheads. Profit is not always a main concern. For the organisers.
I don't know if any let the bus company charge a fare and the liability lies with the co. But we ran on that basis 20+ yrs ago.
Then we changed to hiring in. The bus company guaranteed their hire charge. Its then up to the organisers to set the fares.
The one I'm involved in use a system based on numbers booking on. So very rarely set a price until a few days before travel. It works well for us but it's not for everyone.
Make on some trips and subsidise others.

Re the club. If they hire in. They will have their own overheads.
And purely a guess. (As I don't know their process) could possibly base price on a break even with a set number of passengers. Could be as low as 35/40 (Some bus companies use that as a base figure. For day trips etc.)
It's quite possible the club could use similar systems, either hire in at a fixed price. Or let the coach company take the risk.
If for example only 30 booked on the bus to plymouth even at £43 they would I imagine make a loss. Fill it, and they're quids in.