This restriction applies to surebet punters and other categories of players speculating in bets; because of the restriction it becomes unprofitable to place bets from the account that fell under such a restriction.
This kind of restrictions is not as wide-spread as reducing the maximum sum a punter could bet. It is used by such bookmakers as 1xbet and Olymp. Some players perceive a margin increase as a cheating from a bookmaker, because when the user is not logged in, he is shown higher (initial) odds. Only after logging in the punter notices that the odds had been substantially cut for him. Meanwhile, an increase in the margin at least leaves open the possibility to place a bet, while reducing the maximum bet totally excludes it.