The career should be a secure future where the career should be built around that. One's personal decision is the most important one behind building a career. Many people spend time gambling but they do not prioritize gambling behind career building.
It is possible to build a career in gambling when there are profits from gambling but no losses. But in every gamble there will be both profit and loss but to build a career there must be a guarantee of huge amount of income on gambling. It is not possible to guarantee a huge amount of income on gambling so no one would want to build a career on gambling.
If you are talking about career I think it's very different from a profession, you can actually get a profession in different careers so adding gambling as a profession amongst all others is very possible but will be give less attention or time but then it's still depends on the gambler and it's still possible he could decide to Chase a career in gambling but it will be different.
Chasing a career in gambling will involve some innovation and creativity beyond the regular, let me give further insight, the people who program the slot machines and also create the algorithm for the virtual and casino games are actually career people but then they are not directly involved in placing bets and hoping to be lucky, they are behind the luck you wish for but by virtue of their policies they can't turn this luck around for their selves else the casino bis definitely going to suffer. So building a career in gambling doesn't end with just placing bets and hoping on luck to win but beyond that is still a career.