"snip"
Because it works for him and he's getting results (as in he finished well ahead of Hulkenberg in the standings last year, and barring a massive shock will do so again this year).
"Snip"
and being roundly beaten by Perez hasn't seemed to do much, so he probably does need a change of scenery.
The championship standings do not paint the best picture of comparison between the pair. Perez may be ending with better results but he's far from whooping Nico's behind.
2016: Perez 80 (0 Ret) Hulk 54 (3 Ret).
Of the 14 races where they both started and finished Perez has bested Hulk in 8 of them.
2015: Perez 78 (1 Ret) Hulk 58 (5 Ret, 1 DNS).
In the 13 races where they both started and finished Hulk bested Perez in 7 of those.
2014: Perez 59 (3 ret 1 DNS) Hulk 96 (2 Ret).
In the 14 races where they both started and finished Hulk bested Perez in 8 of them
Its hardly fair to say that Perez finished "well ahead" last year especially when you consider the 5 extra retirements that Hulk suffered. 20 points is also far from well ahead!
When you factor in everything the drivers are quite evenly match and overall Hulk has had the upper hand when it comes to race performances. This year so far has been strong for Perez but he has still had less retirements then Hulk and has lucked in to a couple of podiums.
Both of them would have been a solid choice for Renault, and I think this could be great for Hulk if Renault have a strong turnaround next year.