Because they still saved money. I am not absolving them of letting go of Gould, just understanding why they did it.To answer your question - You were already paying for him in terms of cap space, so why not chalk this past season up to a uncharacteristically bad season and understand when you make that contract you are somewhat stuck with the player for 2-3 years. Whomever you end up signing will just be an added cost at this point.
I agree the 27th in FG% and 24th in extra points isn't good. There's no hiding that. The slight item I'd bring up is those overall stats include dome or warm weather teams, which kick in far more favorable conditions in the back 1/2 of the season. I'm just saying there's a reason why Robbie's best 2 seasons were in San Francisco...
If he would have been on the roster his cap number would have been ~$4M, which would make him in the top 6-8 paid kickers. If he has a bounce back year and is in the top 10 in percentages he's about worth his salary. I'm not saying his salary was worth that production, but rather you were already committed to paying him, so why not give him a chance?
They thought he was on the decline and they were paying him a lot of money.