What's the alternative? Let him leave and sign 2 CBs this summer and have to shell out a 100k a week wage as well as a transfer fee on top of it for someone who might not even be an improvement?
Yes. That's what ambitious clubs do, they constantly try to improve and for that they take risks.
Someone on here (it might have been you, I don't know) once said that there was nothing more PL era Liverpool than not thinking we can improve on our average players, and that Lovren is an example of someone who'll stick around longer than he should. Well, well, well...
I don't even think he's a good choice for the bench. Why? Because you just know he will start a lot more than a normal squad player would. He's sitting on high wages, has a fair few games under his belt and a certain standing in the squad. He's also 28 and has an inflated sense of ego. I mean, he's the guy who tried to score from 40 yards in the dying minutes of a Wembley semi-final that we were losing. He thinks he is that good. He'll exert a pull that most third-choices wouldn't.
At this point I'd rather have Klavan as a third-choice CB (though I'd rather we did indeed sign 2 new ones), because he came on the cheap and never expected to start.
It was the same thing with Mignolet, who had a far, far bigger leeway than Karius ever did (even though Loris deserved it more due to being younger and new to the league). We gave up on our new keeper too soon because we had an experienced and familiar keeper on high wages on the bench. And the crucial problem is that (for me, at least) Mignolet and Lovren will not get any better. We've seen enough of them and they're not good enough. Yet we will see a lot more of them than we should.
Now, I'm not advocating having poor squad options just so our new signings keep starting. I actually think we can have better options than Lovren on the bench that won't have the pull he has, that are younger and cheaper. By having senior players on the bench we will just never get rid of them - they will keep playing a lot of games when we could have been trying different and younger options that might actually a future as starters.
Keeping Lovren is far easier, I'll give you that. But it might be decisions like this that mean we're not advancing as fast as we should have been.