I repair used macs. The number 1 problem on all the pre-2012 MacBooks is damaged ports.
Not for nothing, all of these arguments were made when Apple switched from ADB to USB, to Firewire, from 30pin to lightning, and they're being recycled again for the switch to USB-C.
The answer to your question is that each one does something better than the last in terms of portability or data transfer.
I would do the same thing if I had the same power to move markets that they do - no need to put up with legacies of the past when I can just force everyone to follow me toward whatever I consider the future to be.
USB-C provides zero insertion force sockets, a single replacement for any plug of any kind from monitors to networking, 24 pins, and 40Gbps speeds.
Reliability. Speed. Adaptability. User convenience.
Dropping magsafe is when we started seeing port damage. Most problems on the 2008-2012 models are logic board related.
This argument has never made much sense to me, if only because the amount of money we're talking about is, for Apple, vanishingly small. The Mac is just ~10% of Apple's revenue, of which the "dongle ecosystem" is surely no more than a fraction of a percent.
While admittedly not knowing much about how Apple works internally, I would find it easier to believe that they switched to USB-C just because it looks prettier than because they wanted to make an extra $20 million per year on dongle sales.