PE7 had it, then it disappeared in PE12, and it still isn't in PE13.
Such a useful tool, to be able to build you own list of favorite (or most often used) transitions.
Why the heck would they remove this feature? Okay so maybe some folks don't find it useful... so they can just ignore it if they don't like it. But there's nothing the folks can do if they do like it and it's not available... it all backwards.
Successive version of apps are supposed to get better, not worse.
Best of Breed
Just a reminder, this is not Adobe, rather essentially user to user forum. I have not insider information on Adobe's decisions for its versions and their feature set.
The only way that I know of to address the type of issue that you present is for you to contact Adobe - Feature Request Bug Report Form.
However, if you have Premiere Elements 13, have you updated to 13.1? If so, look at one of the perks of 13.1....Frequently Used category for Transitions.
Details can be found in the description of the 13.1 update offerings.
Please let us know if the 13.1 Update Frequents Used works for you for the purposes that you describe.