If you look past the long term commitment of say 6 or 7 years and think at some point we could trade this pitcher/player. Why not take the plunge? IMO it's a way better alternative than dealing top prospects and trying to extend 30- 30+ year old pitchers who are looking for 4 & 5 year extensions.
As for current payroll?
Rasmus better be gone, Morrow could be gone, incoming TV money of what 25m, big money coming off old player contracts in subsequent years. How can't they afford that going forward?