I don't have a problem with people saying GGG should consider it, but Lara is not the end all be all. I just don't think that highly of him. The key thing here is that his mandatory is with the IBF and they actually enforce their rules. I haven't heard anything definitive, but it sounds like unless he got the Canelo fight, he was going to be required to take his IBF mandatory or risk being stripped and that risk is very real - see Tyson Fury. The difference is that Fury said he didn't care about the belt so he did nothing to try and keep it. GGG has stated that the belts and total MW unification is important to him and so far all his moves have indicated as such, so an IBF defense is greater than a fight vs. Lara. The other two belts are with Canelo and BJS and those are the two fights he clearly and vocally has pursued.
Again, people may not be impressed with the IBF mandatory, that is fine, but he is doing exactly what he has said he would do - go for MW unification and to do so is bigger than just Lara. People are comparing Lara vs. IBF mandatory. Not the argument. Keeping the IBF to go after BJS and Canelo is what people should be excited about. A fighter going after the other best fighters in the division and wanting to be historically relevant by being unified champ, what a concept!