Hi Darth
There could be a number of reasons why this is, but I would expect the main reason that you tilt online when you wouldn't tilt live is that when you play live you are perhaps more in control of your emotions as you have real people around you and therefore either consciously or sub-consciously, you manage the situation better so that people don't get a read on you, or you simply show more respect.
In online poker, there is no one but yourself to control your emotions and no one impacting on how you behave. I base this on , think of all the crazy things that people say and do on social media, that they would never dream of doing in the live world, ie when face to face with the person they are talking about or behaving to,
I think it is a case of merging the real world with online and behave online how you would in real life.
To help, here is a link to a Cardschat article that may also assist you manage tilt.
https://www.cardschat.com/beating-tilt.php
Good luck
BentleyBoy