There's years worth of data suggesting that working out at the combine is not a net positive for any player figured to go high round 1.
Potential negatives far outweigh any slight bump. You also risk injury.
Just not worth it.
The potential negatives are part of the point. Some feel that not participating means you have something to hide. If the negatives are there, they will materialize eventually. I cannot think of any high rated prospect that harmed themselves participating in the Combine. As far as the injury thing goes, they could injure themselves working out on their own doing some of the same activities they are asked to do in Indianapolis, almost an irrelevant point. A Pro Day workout only indicates there is something that they are hiding and it requires more digging.
The NFL is making a lot of money off the combine via sponsors and TV so of course they push hard to have the guys compete.
Any decent scout will state they could care less as they already have a grade on those guys.
GM's might like it so they get a first-hand few in one week but they generally have NOT held it against them.
Most of this is driven by agents. Of course the scouts do, but again, they are funny about it and if you asked most of them, yes, they prefer the prospect be transparent and do everything. And there are examples of it.
Bill Parcells would set his boards prior to the workouts and that any movement, up or down would be tied to them and the scout's making the decisions.
If you are a competitor, you do it. All the teams are there and if you are neck and neck with another prospect, they like to see how you compete. Pro Days are a backup to reinforce what happened at the Combine, or in some cases, recover. A disastrous Pro Day, while scripted to be in the prospect's favor, can really hurt and it is one shot only if you skip the Combine.
Mariotta and Winston both participated but did so with little movement. Winston was the better thrower and Mariotta the better athlete.
How much could they move if they did okay? They were pretty much oneA and oneB to begin with?
Luck and RG3 both declined to throw at the combine. Carr and Bridgewater didn't throw. Bortles did. It's been hit and miss.
Luck could have sat on his couch and got drafted at one. He was not jockeying for much of anything. Carr and Bridgewater skipped it and it nearly cost them both first round status (Carr fell into the second). Bortles went higher than projected. If it is hit or miss, these examples suggest you are probably better off, especially how the position is so valued and hard to evaluate.
For guys fairly certain they are top 5 there is little to gain and a lot to lose.
I am not certain that Goff is viewed as a surefire top 5 pick, much less head and shoulders considered better than Wentz or Lynch. He might need an extra nudge and I am sure his agent probably has an idea of that which is why he is not advising him to hold himself out.
All in all, I think he's doing the smart thing.