What planet are U on ? Try halving your figures to be more realistic !!
Not that I like sticking up for stealers too often, but I would guess £20k - £30k is more likely wages ranging from a just qualified tech, to a fairly senior technician, I would expect regional variations as well, but at I can't see too many bike mechanics making £40k
There is normally a building which eats up money in rent, power, heating, rates etc. and BMW ones are bigger and "better" (or at least more expensive) than most
Then whoever picks up the phone to take bookings / answer stupid questions will not be bringing in any money, or if this is done by the mechanic it is dead time...
As is ordering parts, keeping the workshop clean and tidy, and any training (which may also incur a cost on top of lost time) and then holidays and sick days are paid for.
From experience in the trade I would say your doing well to (Honestly) book any more than six hours on a good day, and on a bad day you can have mechanics sat around earning nothing, this is where the bonuses schemes tend to kick in and turn honest folk into thieves as they need to bill 9 hours in an 8 hour day to earn a fair crust.
I think the £80 - £100 (+VAT) of most BMW dealers is excessive, I have a mate who is a truck mechanic and points out you can get 18 wheelers serviced for less per hour than most main bike dealers charge, and the space required to service a truck is significantly more, and the tools are also considerably more expensive.
£100 - No thanks, but if someone is charging £50 an hour for a qualified technician and doing a good job from well equipped premises your doing well IMO.