Sorry for the obvious answer here, but though everyone has strengths and weakness, you do get better at what you practice well and after 20-30 years of practice, your skills reflect first what you worked on most.
In this bunch, I am good at sight reading, good at reading notes, can
only memorise with both hands; bad at rhythm, bad at memorising.
One possible explanation among others to your situation:
The memory most people have (and the first to go away when under stress) is finger memory. It comes from playing the piece over and over and doesn't require much understanding of the piece. If you are good at sight reading, chances are you quickly play hands together and thus acquire that finger memory. And chances are also that you rely on the music sheet heavily (since you read well) and don't have to challenge your memory.
Bad at memorizing can mean many things: that it goes away with stress, that it takes a long time to come to you, etc. Take a short piece and explore a different approach: practice it diligently with hands separately for a much longer time; try to play it from memory after just a few passes, even if you don't know it yet; then as you start playing it from memory, start randomly from anywhere in the piece, and chances are that you will find yourself having a very strong memorization for that piece, pretty quickly, playing it with both hands or only one hand.
My point here being that even though everyone has different inherent skill, I suspect that a lot of what you consider as a given comes from your playing habits.
