On my last two flights I used my phone to measure the angle of the table on the ground and in the cruise. (Bit sad, but you need to make your own entertainment sometimes).
Sure enough on the first it was dead level on the ground and pitched towards me by two degrees in the cruise. On the next it was already pitched towards me by two degrees on the ground. Clearly over time the table gets worse.
But why on earth design it to be level on the ground, where nobody uses it?
Next time you're on a longish flight, measure the table angle at the start and end of cruise. They will differ.