Worrall
Roach
Overton
Lawes
Atkinson
J Clarke
Curran T
Curran S
C Jordan
C Mckerr
Dunn
Barnwell
Topley
Taylor
Fisher next season
On that basis, you've forgotten Spencer Johnson, who only plays in the T20 games.
I have no idea how it works contractually and how they're actually remunerated, but here's my take on the blokes in your list.
Worrall - there's talk of him being picked for England when he qualifies next year. And he is 33 now.
Roach - getting old, as he has just turned 36
Overton - never bowls due to fitness issues
Lawes
Atkinson - looks like he'll be playing for England or under instructions to be rested
J Clark
Curran T - only plays T20s for Surrey as he has retired from red-ball cricket.
Curran S - only plays T20s for Surrey. I don't think he's retired from the red ball game, but he's hardly ever available for the CC.
C Jordan - only plays T20s for Surrey. I think they only sign him for The Blast.
C Mckerr - only plays in the 50 over cup because he isn't good enough for the CC or for the T20s
Dunn - only plays in the 50 over cup because he isn't good enough for the CC or for the T20s
Barnwell - very inexperienced, has played in the 50 over cup without giving any indication that he's good enough for the CC
Topley- only plays T20s for Surrey. I think they only sign him for the Blast.
Taylor
Fisher next season
Looking at it like that, you can see why they've signed Fisher, especially for the CC games.
And although there are a lot of T20 specialists, much of the time they're playing in franchises elsewhere.