Exactly - it would be a complete pain in the arse and they know this and are banking on it.
There was a time until recently when it was considered 'fact' that online casinos could take the utter piss with their T&C's and the customers had to suck it up. For those fortunate to gamble at UKGC licensed casinos, the regulator called in the CMA who sided with the consumer and took a number of enforcement actions which fundamentally changed the game to the players benefit.
The following page provides some long commentary on the matter:-
In regards to your specific problem the following section is an interesting read:-
(4) Fairness and transparency of play restrictions
The issue
In addition to our general concern that significant conditions are not adequately communicated to consumers, we are also concerned about the fairness and transparency of specific terms which purport to set out restrictions on particular types of gameplay.
Some of the more specific examples of such terms seek to prevent consumers from placing wagers above a certain maximum bet size. However, more nebulous and uncertain terms talk more broadly about consumers not engaging in ‘low risk betting strategies’ or otherwise behaving in a manner which the operator considers to amount to an ‘abuse’ of the promotional terms.
In circumstances where there is nothing to stop consumers inadvertently engaging in such behaviours, and operators may exercise their discretion with serious consequences for the consumer (including forfeiting winnings and unspent deposit funds) the CMA considers such terms are not fair or transparent.
The underlying principles
The CMA has a particular concern where such terms could be used to apply sanctions to consumers’ own deposited funds, as appears commonly to be the case in the promotions we have seen. Such promotional terms operate to prohibit and sanction play that would otherwise be permitted and legitimate when the consumer plays outside the promotion, including placing bets above a particular threshold.
Whilst there is no overarching ‘right to bet’,
once an operator accepts a bet there is a binding contract and the winnings constitute an enforceable debt. A term that seeks to legally reserve an operator’s position to
avoid liability under such bets on the basis of play restrictions would cause a significant imbalance by departing from the legal position that would otherwise apply.
Unfortunately, those comments are highly qualified opinions which ultimately have to be tested in a court of law. My interpretation is that by allowing you to place that bet they legally accepted your bet. My guess is that if this was tested in a UK court of law the confiscation of funds may not be lawful. But back to your point - who wants to go through that process?
And for those who make daft claims such as "it's in black and white in the T&CS" that is simply not the case in UK law. If they had a clause which stated you had to give them a kidney if you bet more than £5 do you think they could legally enforce it? Of course not. Thankfully we have good consumer protection laws in the UK so they can write what they like in those T&Cs......as long as they are fair and legal.
Sadly, the biggest heist the online casinos managed to pull in this regard was convincing everyone it was entirely legal and you end up with a situation where even people who are players and not even affiliates do the casinos bidding on their behalf much like a lot of responses to this thread.
I can honestly say that if the outcome of this for you is that you never play at an online casino again it will definitely work out better for you in the long run.
All the best.