There is maybe hundreds of different shileds in the market. I had a project in my mind and bought the shields I tought I needed. Every single shield works fine with my UNO If I try to build a system, there is problems.
I want to have NET, SD, MOTORS and LCD Net connector is so fat, that no other large shield can be used with it Motors shield does not have GPIO connectors on top, so no LCD shield in this stack SD shield is short and the slot is towards USB connector. The SC card can not be reached, if I use LCD shield. And in any case it is impossible to have LCD and proto-board in the same stack.
There should be some standards for the 3rd hand markets how to design the shields.
In the far history of computing I built a board serie for laboratory use. I used a normal IDE flat cable as a backplane. if you needed another card, you added a female connector to the cable. If you wanted to measure some card, you just opened the right page from 'the book' of cards. To prevent echo, we had cards with resistors in the end of the bus. One of the cards was a swithing power source.