The two don't have either the same scholarly traditions or the same aims :) Grounded theory aims at identifying variables and often quantifies their presence in research materials, which RTA does not. It's also based on the constant comparisons between cases, which RTA isn't. Constructivist Grounded Theory is a great book!
Thinking back on this question: The very reason for which RTA was developed in the first place was to be more flexible, in its aims, that other qualitative analysis (grounded theory being arguably a qualitative/quantitative approach). RTA really emphasises the interpretive work of the researcher, whereas many ‘schools’ of grounded theory are more objectivist — in the case of constructivist GT, the quantitative approach remains, although the epistemological background is different.
Then GT aims at developing theory. TA can be more descriptive.

I do agree however that, with time, some version of TA (codebook approaches, framework TA etc) feel closer to grounded theory than they used to, but I think it’s mostly due to a shift in the research landscape towards more quantitative approaches of qualitative research.