Actually TVB can still adapt works from other authors (Wen Rui An, Gulong, Huang Yi) other than Jin Yong's works but the past results haven't been that great as they failed to achieve good ratings. Considering TVB puts a lot of effort and money into producing these dramas it's actually a big deal. TVB is really cheap I heard and employees work 16-18 hours a day filming with little sleep, and on the fly script. No wonder so many artists left TVB and headed for Mainland instead. It's sad but reality. Sheren Tang, Steven Ma, Charmaine Sheh, Bowie Lam, Maggie Cheung, Eric Suen, Gigi Lai (retired from acting), Kevin Cheng, Felix Wong all have left TVB. Artists like Sheren Tang, Felix Wong and Maggie Cheung criticize the company straight up and have a strained relationship with the company now.
Personally I am not a big fan of Mr. Huang Yi. TVB produced A Step Into the Past, Lethal Weapons of Love and Passion and Twin of Brothers based on his novels and I didn't like any of them. (TVB had to change all the details in the stories because they were too long and included A LOT of sex). This author sounds like a pervert to me to be honest. On Lethal Weapons of Love and Passion TVB spent a lot and the ratings were horrible. The storyline was not even that good to begin with. For god sakes Sonija Kwok and Charmaine Sheh are both older than Raymond Lam who is the main lead.
I was okay with Mr. Wen Rui An's works. TVB produced Face to Fate (based on Shen Shuang Li Buyi), Strike at Heart and The Four (based on Sida Ming Bu aka The Four Constables series). Of course they never stick to the novel (why I wonder, why produce dramas from authors only to change the storyline and characters completely, why not make your own storyline then) and again failed to achieve good ratings.
TVB produces mostly ancient dramas based on Historical series now. (mostly Qing Dynasty with shaved heads or queens battling over power). And these dramas don't use martial arts as an emphasis either but I guess that's what people look for because TVB just can't produce proper ancient wuxia serials anymore anyways. But with all artists leaving the company and so many newcomers joining I don't think the results would be good even if they tried. Imagine if TVB were to adapt Legend of the Condor Heroes right now, no one is a good candidate at all for the lead roles I can honestly say.