I am trying to find the advantage for the ecosystem to do that, since effectively, less SPS would need to be burned to mint DEC.

If people spend the same amount of DEC (on CA, wild pass, whatever), less SPS is burned and that would not be a good thing for the ecosystem, because we want SPS price to go up, right?

If the same amount of SPS is burned there is more DEC around. Everything and anything needs to burn DEC for the benefit of the ecosystem. So, more DEC minted is the opposite of that and that would be bad, right?

Well, we could assume that with burning SPS being a more attractive value proposition more SPS is burned overall to get more DEC to spend. So effectively a discount is put on everything and anything, as long as you pay in SPS of course. But wait, credits are 1 USD : 1000 credits (lets for simplicity say 1000 DEC), 1 USD worth of SPS is 975 DEC and would go to 995.

And that is the quintessential thing this change would do:
It makes paying with credits less advantageous compared to paying with SPS, although credits are still better. Is this good? The short answer is, it depends. But this is what this vote is about:

Do you want SPS to have more buying power and make it more attractive to buy stuff with SPS instead of credits.

P.S: All of this only is a topic if DEC is at peg and 1000 credits == 1000 DEC.