To me it's simple arithmetic, why a bookmaker bans a consistent winning customer.

Both entities, ( Punter and Bookmaker ) may have limited or unlimited funds to bet with.

In the case for example of the constant winning punter the funds are from winning.
The bookmaker in pure bookmaking terms their funds come from ( not counting ads and sponsorship based funding ) what's been wagered by ALL punters on race per race basis.
To illustrate where my wording may not make sense, but the numbers do;

MR 1
it's a 12 horse race
All runners have been betted on, so the bookie has collected let's say $100,000.00 in total from the betting public one way or the other.

Then, a couple of proffesional punters well known to the bookie come along and put on large bets, knowing the horse will win,
today, @ ~ 7/1.

The race is run, the professional punters win and expect the fixed price payouts to be paid.

The bookie has to pay.
( but they have been paid in total in excess of $100,000.00 )

The bookie actually losses, the money the bookie has to pay to 1 or 2 winning professional punters exceeds what the bookie collected in total for that one race.
Not counting the smaller punter with their $10 or $50 winning bet has to be paid to.

What then does the bookie prefer ?
The winning punter with a $10 to $50 bet, where the payout won't break the bookies bank ?

See what I am saying here, the pool of funds on a specific bet in it's own right is not enough to pay the professional 1 or 2 punters who go for broke at each and every bet.

Just my bet's worth.
( although I am an advocate for the punters, but when viewed purely and unbiased from a arithmetic point of view the numbers don't add up for a bookie to stay afloat.

So the bookie has no other choice than to ban the bigger known winning punters, and allow the smaller winning punters see the end of the day with a pocket full of cash,
and the losing punters keep on keeping on.