You didn’t mention the construction of the carriage. Now days most carriages are made of thin flat pressed metal cantilevered from the external depressor. Nothing holds them on the opposite side.
In the old days, the carriage/platforms used to be more robust, and there used to be a vertical wire inside the back of the toaster and the carriage/platform used to slide up and down that while providing support.
I have written previously about multiple toasters we have had failing (from metal fatigue?) where the thin pressed metal carriage/platforms enters the body of the toaster to connect to the external depressor.
I think that because there is no support for the carriage/platform on the back of the toaster it flexes more than the front, and with time, it gives up. Obviously, this depends on how much toast you put through, and whether the bread slices are heavier or lighter.