As parent poster wrote, we like nostalgia, because we clutch to our experiences. We compare them instead of collecting it. On the other side the more we experience something the more we stall or get bored. Even with other people - with increase of lifespan we also increased number of divorces, lost connections etc. That doesn’t make us happier.
One could argue that we, as humans, suffer more today from out deteriorating bodies, than people in medieval time, when it was shorter, and that we suffer more psychologically due to increased influx of information, global conscience and artificial constructs we build every day.
Resources would also be an issue, so even if immortality would be obtainable it’d be either reserved for the richest or would divide people with almost impassable line splitting centuries of servitude and centuries of indulgence.
So to answer your question - why not? Because it’ll bring suffer to many on many levels except for a blessed few and we should focus first on making life great for everyone present before trying to make it infinitely longer.
Joking lightly (as subject is very deep) - it’s somewhat useful skill to know when to get off the stage.