Why do we put animals to sleep, but humans are expected to suffer until the very end?

There was that euthunasia dr. from Michigan back in the day. To take cancer patients and maybe some elderly, all very willingly, away from the suffering they endured on a daily level. That was shut down quickly.

When our beloved pets are sick beyond repair, we take them out of their misery, out of love and respect. We dont want them to suffer.

Do we respect our pets more than human dignity?