Stealing third is a weakness of SOM in my humble opinion. In fact, when I googled the topic, here's what I got:
Also of note is that the MLB-wide success rate since 2015 is much higher stealing third base (77.3 percent) than second base (71.4 percent).
I believe this is because a runner won't steal third in real life unless he can get a great jump, not because it's necessarily easier. Although, Joe Morgan has been quoted as saying stealing third is easier.
Regardless, SOM makes it harder to steal third with less chance of success than for stealing second. Unrealistic.
I wish there was an option in SOM 365 to "Steal Third Less." Or even better, come up with a better in-game formula that makes it difficult to get a jump to steal third but better odds of success if you do.