A competitive esports scene for GTA Online would be interesting to have, but it would ultimately be unrealistic.
Competitive esports scenes can generate a lot of attention for video games. With more attention comes more money. Esports tend to start off as a money sink for companies looking to market their games as competitively interesting. However, GTA Online doesn't lack an esports scene for this reason.
GTA Online doesn't have a competitive esports scene right now because the current game isn't esports friendly. Esports have to be interesting for players to watch, which isn't something that can be said about most of GTA Online. Unless there is more focus dedicated to a competitive new game mode, there will be little interest in seeing competitors compete against one another in GTA Online.
GTA Online in the competitive esports scene
It would be highly unlikely for GTA Online, as it stands now, to have a viable esports scene that would generate profit. Right now, GTA Online is massively successful, so it's not like Rockstar needs an esports scene to make the game stand out from its contemporaries.
If anything, a competitive esports scene might hurt GTA Online's reputation. A poorly-handled esports would be a net loss for Rockstar, which isn't ideal for a business to have. Considering GTA Online's marketing is already phenomenal (it is one of the most played games of all time right now), having a competitive scene would do little to help boost players' awareness of the game.
Some reasons why GTA Online could succeed
The main reason why a GTA Online esports scene would succeed is because of the game's popularity. It's one of the most played games right now, which means that there will be an immediate audience for any esports scene if attempted.
GTA 5 is also among the most-watched Twitch categories (largely thanks to GTA RP), which is the same category GTA Online falls under. If Rockstar gives an incentive to watch whatever esports event they make, then there will likely be thousands of players willing to watch it. Even if people are AFKing, their views still count as a regular person's.
Some reasons why GTA Online wouldn't succeed
GTA Online isn't like other popular esports-friendly games like Overwatch, League of Legends, or CS: GO. It's more comparable to a game like OSRS, where there is a lot of grinding before players reach a competent state for PVP. While OSRS does have some success in esports, it's still largely seen as a joke compared to other successful esports scenes.
GTA Online would have to forego all of the regular grinding and put players on an even playing field to make it interesting for spectators. Otherwise, some players will have a distinct advantage outside of a meager skill difference. Successful esports tend to replicate the formula regular sports do, except in a virtual setting.
As it stands now, GTA Online isn't a competitive game. Ignoring the obvious impact that Shark Cards have on the game, what would fans even want to see from GTA Online? Heists are fun to do, but there won't be many variations between seeing one person do it from another few dozen. Likewise, other missions are fairly barebones and would make for a terrible viewing experience.
Racing and other game modes would be the best option for GTA Online if Rockstar really wanted an esports scene. GTA Online racing can be fun, but not so much that it would make for an exciting esport. Likewise, other game modes have received so little attention from Rockstar that they would require substantial updates to interest players again.
How GTA Online could become more esports-friendly
In the highly improbable scenario where Rockstar wants GTA Online to be a viable esports game, they will have to introduce new content in GTA Online. More specifically, it should involve putting players on an even playing level. After all, a game can't be competitive if the richest person always wins.
While that works in real life, it's not as interesting to see in a video game. Rockstar can create an entirely separate mode that uses something like Deathmatch or Last Team Standing, where all players have the same stats.
Of course, those game modes do exist right now (without fixed stats), but they're not popular to play. Having a competitive game mode would require too much effort to make it work, as players would either choose to grind for money in the current casual open lobby or they would try to be pros.
Predictably, most will fail in the latter. Eventually, fewer and fewer players would try out GTA Online esports, which would also correlate with fewer people watching it. There are ways for GTA Online to work as a possible esport, but it's simply not worth the effort right now.