I found this in their ToS:
10.1 You are allowed to place Your bets/wagers on the markets/products offered in the Website. Stake is not obliged to accept any bet/wager from You and bets/wagers will only be deemed as valid and finalised, and therefore as accepted by Stake, when You receive the confirmation from Stake of the acceptance of Your bet/wager.
Maybe it doesn't explicitly state that they can limit account but it still gives them the right to reject any bet they want such as a bet which exceeds a certain amount.
For the record, I do not endorse such practices but we can't deny most sportsbook do it and they do it mainly to protect their business.
See here, great informations about the practice of limiting users !
ANJ concluded that operators cannot refuse bets from a player, unless the operator has a legitimate reason as designated under article L. 121-11 of the French Code of Consumption. This means that an operator could argue that it has a legitimate reason not to accept a sports bet from a patron.
Legally defined legitimate reasons include refusing to allow a minor, someone who has self-excluded or an excessive bettor to gamble.
In addition, offenders could receive two years in prison and a fine of €300,000.