It is true that high salaries are the key for top European players like Neymar to join the Saudi Pro League with Al Hilal, there are many reasons behind this transfer process. It is reported that Neymar is no longer wanted by Luis Enrique, and is currently at odds with another PSG star Mbappe. But I myself can not confirm the truth of this news, at first glance I think it makes sense.
Neymar presence at Al Hilal further complements and sharpens their attack line, for the adaptation process I think Neymar will not find it difficult, except for being hit by an injury.
Saudi clubs are just trying to make news and get enough attention of the football lovers with money and huge signings. To be honest I feel like they are still far from getting to a level where PL and other league competition is.
As for Neymar, good for him as he is getting a huge contract as his career was becoming more and more uncertain at PSG. PSG is kinda club who ditches player too easily. Also there wasn't a club interested like Al-Hilal with huge proposal. It was obvious where he was gonna go and it was a perfect time I would say for Neymar.