If you take his record breaking season as an example, I think hardly anybody was expecting Benzema to stay on that level. That was so unreal when he scored all those impossible goals and decided the games again and again. But in the last season he wasn't a critical factor anymore. They already had to find alternative ways to score their goals as it was too risky to believe that they could fall back on Benzema when he is needed. They can now focus on signing a superstar striker and that is what they are aiming for with Mbappe, but even if it is not him I doubt that they are ok with Joselu only. He is not the one they are really looking for.
Everything that Benzema has done is a beautiful memory to remember when he scored many goals and became decisive for Real Madrid in the previous season. Now his era with Real Madrid is over, we even saw a fairly harmonious farewell when he parted ways with Real Madrid. For next season, Real Madrid's front line will own other players, even Joselu is likely to prove the quality he has for next season.
Apart from that, Real Madrid also wants to bring in another sticker in this transfer window. Mbappe has become Real Madrid target this season because at his age he is still very young and skillfully he has everything to become the next Benzema next season. Real madrid may need a sizable amount of money to bring in mbappe from Psg.
I don't know that much about Joselu, but he is not exactly the player who is poisoned to fill the gap that Benzema will leave.
The fairly harmonious end was also due to Benzema not being at his peak anymore and Real Madrid noted that. It was ok for them as they would save his salary and Benzema let everyone know that it wasn't for the 200m or whatever he is making over there, but because he is Muslim... I would also feel plenty of harmony when someone were to write me 200m cheques for kicking a year or two in acclimatized stadiums.