I agree that it's weird the Spurs haven't signed Morris yet, but we don't know the whole story. I highly doubt they wanted to lose him after trading Bertans...who, btw, was a perfect fit for the Spurs.
No matter what, it's a 'bad look' as the kids say for Morris. Even if he stands to make a little more money (the TX non-income tax is a good point), it still more money overall. I guess he will be a lot closer to home, if that matters to him.