Why is my Gabor patch not resizing as a function of the bounding box?
The size parameter in your code simply means the size of the patch, i. e. the interval in x and y over which you sample your Gabor function.  What you are thinking of is the support of the function, i. e. the interval where it is noticeably different from 0. This is determined by the sigma parameter, which is the bandwidth of the Gaussian.

So if you just increase size, you will get a bigger image back, but the area where you can see the ripples will stay the same.  If you increase sigma, the area with the ripples will get larger, and then you may have to increase size as well to see all of it.

By the way, IMHO, the right place to ask this question is on dsp.stackexchange.com.