Icahn for sure just invested so he could be higher in a liq pref stack than A16Z, so when things go south he can take away anything that A16Z could have potentially recouped
There is a theory that Icahn is so rich and old that the money doesn't really matter to him much anymore. Instead he gets the most value from investing his money in ways that entertain him and sometimes that's by poking people he doesn't like in the eye (Ackman, Andreessen).
