There's even casinos you an play against limit players.
The real "challenge" if you call it that is finding No Limit solved.
I could easily code a No limit bot which will make the right move maybe 80-90% of the time that puts reads on and everything.
But where's the fun in that? Online poker sites crack down on bots with captchas, so why do I want to lose my initial deposit. Anymore when I play no limit, I play it like it is solved. I get my money in correctly maybe 95% of the time. The fun part of poker is that once you know how to play, its simple. Its hard to learn how to play correctly, but it is easier than tic-tac-toe once you got a strategy down. And yes, I've turned $1 into $1000 over several thousand games, so I'm not just bsing. I'm just a lifelong gamer with a math statistician background who got interested with poker over about a decade.
The reason I don't just go and make a living over it is that I still have some moral hangups on making money and not producing anything for society. It is the same reason I didn't decide to be a pro-gamer, but instead wanted to make software games and useful aps for people to use.
The only thing a good NL bot could do in today's world is make bad players into geniuses like chess programs makes everyone online play like a Grand Master. And there's no good way to monetize this with piracy or I'd sell "near-perfect No limit poker bots" for 500$ a pop or something. Since there's no money to be had due to piracy, its the same reason good players don't write books on the best strategies, they can just play the game and make money. It's better to keep other poker players in the dark on the right moves instead of educating them. I only teach a select few how to play the game right, and normally they don't listen anyway :P Some day in the future everyone will be playing perfect NL Texas Holdem, and it will no longer be a game of skill, it will be gambling since everyone is playing the same style.