
No-one knows what critter the avocado fruit . . .
. . was developed for. All they know is that it is extinct, must have been huge to swallow that pit, and required a lot of energy.
For a fruit to convert starch to sugar is no big thing, but to convert all the way to oil takes a considerable energy investment - so there must have been a very good reason.
Today, the one critter (other than people) that Loves avocados is Jaguars, but they don't spread the seeds effectively. Today the trees depend on people to spread them, and that has been quite successful for the trees.
Florida avocados are relatively low oil - you can't make guacamole with them, only "avocado dip" which depends on sour cream (guacamole contains NO sour cream). Today most Florida varieties are crossed with Guatemalan and/or Mexican varieties to partially fix that problem.
Florida avocados can only be grown in a hot wet climate like southern Florida, so most of the world plants Guatemalan or Guatemalan/Mexican hybrids.