I'm sure it's more about studying pitchers' moves and picking your spots than about speed. He has tried to steal 55 times. Elly has had 80 attempts. The more you steal, the more likely it is you will get caught. I think also that, as you pointed out, the most SBs he's had before this year is 26. Perhaps he was being overlooked as a SB threat. He also hasn't pitched this year. My guess is that when he starts pitching again he will not try to steal as many bases.