ciao Remix1019
Well, components need space inside the device. If you want to fit more, the phone gets bigger - or you cut back on other components.
For example, the A72 has a 500 mAh bigger battery than the A71. The cameras also look bigger from the pictures. So, with practically the same product dimensions, you either have to a) make it a little smaller or b) leave something out. Alternatively, of course: thicker and bigger.
I wouldn't mind a thicker phone with a bigger battery ;-)
But sure, I can understand you. Luckily you have a choice and can still buy the old model :-)