That's part of what they do, but they are more than that. I'm not arguing that the Iranian government is democratic or non-tyrannical; however, the IRGC is responsible for more than internal regime stability. They have air, ground, and navy forces, as well as an intelligence arm. They are an integral part of Iran's defense as a country. You can't harm or sanction the IRGC without sanctioning Iran itself.
Sanctioning Iran--and other regimes in the region and in South America--more often than not results in decimating the population and eroding the middle class (which is your best bet for a transition into a democratic government/regime, but the change has to come from within. You're going to help the regime, not harm it.
And again, the hypocrisy is flagrant. Israel commits and has committed far more crimes than Iran ever had. From its genocidal inception to and refusal of the Palestinians right of return, to their repeated atrocities before, throughout, and after every war in the region. They've always killed civilians and especially children. They are proud of their terroristic ways (e.g. the recent pager attacks in Lebanon). Their "settlers" have always terrorized Palestinians. They openly talk about assassinating enemy leaders.
Where are the sanctions imposed in response to any of that?
I searched using the name in the bottom-right, and he/she is a developer who created an open source tool to construct the graph from historical GitHub incidents. It's hosted here and the source is here