a tv is "good enough" to show tv. as in only needs a rather low refresh rate, response time and so on to make sure the tv looks good. no reason to make it capable of doing more.
however, a pc requires a lot more from it's screen. this is why they cost more, because they do more with better parts. i'm sure they could design a tv to do the same but you'd not find a 65" 4k one for $600 anymore. they'd cost a lot more. basically the same as what a pc monitor costs for it's size and features.
so can you use a tv as a pc monitor? absolutely, no problem at all if it has the right input for you. however, will it perform like a pc monitor in games and other intense duties? not a change. will it handle browsing, streaming, light gaming? sure will if you don't get bothered by the lower detailing and such.