Do you have any evidence to back up this claim? My understanding is that they have plenty of basic barriers in place but bots have become sophisticated enough that they're no longer able to prevent/detect them with the simple stuff.
Also, the community seems to believe that Venezuelan gold farmers are typically not bots but instead real people doing simple tasks on multiple accounts at the same time.
Anyone whose looked into OSRS botting from the perspective of the botters knows that the "Jagex isn't doing anything" meme is not actually true. It's very easy to get banned and bots have to go to all sorts of absurd means to not get banned quickly and emulate human behavior. Botting tutorial island can even get you banned, which is saying something since bot scripts have had over a decade to evolve.
Now, could it be better? Definitely. But ultimately without locking down the game client more, which would alienate the majority of the playerbase who uses third party clients, it is very difficult to effectively ban bots at a scale that would be appreciated by the playerbase. In just a couple days you can implement some botting capabilities through client plugins, popular bot software has years of manipulating the client, so without a major change to the client it's very hard to ban bots.