IMO the reasons for the Seahawks in particular signing a lot of one-year players has nothing to do with motivation or comp picks.
There is a sea change coming, so to speak, over the next two years. The org wants as much flexibility as possible to carry out this change to maximum effect.
The org wants to figure out what it has in the young OL it's invested all this time developing. We no longer have the underpaid RW advantage with contracts. If the young OL pans out, and I actually think it will (Fant and Gilliam included), we'll have a similar advantage via OL. Last year's sucktitude was a high price to pay, possibly costing us a strong title run, but that investment may start to really pay off this year. If they sign a prime vet to unequivocally take one of those spots for 3+ years and the young guys develop as expected, you waste that advantage.
This draft has a very deep talent pool. It's critical the Hawks pull out a good draft. If they do it's very possible we get 6+ future starters out of the draft and UDFA this year. We nail this draft and keep Wilson healthy and we have a Patriots-like SB window. We just need enough to get us through 1-2 years of transition while the young guys turn in to starts and pro bowlers. So these 1-year guys hold things down and give the rookies a year to develop before they're thrown in to prominent roles.
Lastly, the big contracts are ending - either they expire, are extended, or terminated a year early to open cap space, all dependent on the performance and prospects for future performance of each individual player. JG, Kam, Avril, Sherm, KJ, Earl... along with mid-level contracts like Kearse and Lane. The team will keep who they want, let the ones they want go. They can open up oodles of cap space if they want to splash in FA - not on the Cary Williams of the world, but top players who carry little risk of performing poorly.
It's gonna be big. This is the last year the team will make a run before big changes happen. The Seahawks have a solid chance but they weren't gonna mortgage the future for 2017. Title or no, everything will start changing dramatically after this year.
It's brilliant planning by Pete and John - lining all this up perfectly. The key is pulling it off, and the first big part of that is this draft.