Is there a reason to start this new model name vs simply calling it the 2020 "eGolf"? Is the eGolf basically a hack design and the ID3 a true, ground-up electric design?
That would be my interpretation. That the traditional Golfs and Tiguans will continue to be delivered with ICE/Hybrid drivetrains but that any pure EV model of an ICE car would always be a compromised design because of how radically different they can be built. So even if they make the ID look like a golf in the body it’s a radically different car, and if they still make the golf they shouldn’t be selling this under the same name. As the article says, the interior will have much more space for example. Calling it eGolf might be confusing, and might be underselling it.
From the article:
"The ID.3 will be the first car built on the Volkswagen Group’s “modular electric toolkit” or “MEB” — a technological platform for EVs that includes the battery pack and motor."
That, and this not the only planned vehicle based on this platform, so "eGolf" would be a bit restrictive.
I would say a lot of it comes from it being a completely different platform. Most likely there will have a line of cars with similar names kind of like BMW's i series that will encompass all the electric vehicles made on the platform.
Volkswagen is positioning this as the 3rd era of the company. They started with the beetle, then the golf has been the backbone of the company for 40 years, and now the ID.3 is going to be their core identity.