Uh, wake up yourself?!?! PDF is OLD technology, and though it will never be obsolete, it is archaic and barely functional.
As has been stated, there are much better digital formats than PDF, and 5E is available in several of them with DDB, Fantasy Grounds and Roll 20.
no need to pay for a regular subscription on top of what you've paid to get the book in the first place
It offers things PDFs do not, but it doesn't fill the need that PDFs fill. It's a proprietary service to which you subscribe, and that require you to be online. A PDF would be a book, in electronic format, that you can read on whatever device you want. What's more, as with the physical book, you buy it, and then you have it; no need to pay for a regular subscription on top of what you've paid to get the book in the first place.
The existence of D&D Beyond does nothing to reduce the need for PDFs. It's a whole different thing.
...and you know what format you still can't get the core books in? PDF! When is WotC going to realize that we're in the second decade of the 21st century? That all not having PDFs does is hurt their sales. You get people like me who have ignored 5e altogether because of the lack of legal PDFs. Then you get the people who might have purchased a legal PDF, but because it wasn't available, found it another way. There's no way that the unavailability of legal PDFs fights piracy; it just inconveniences and/or drives away their legitimate customers.
WOTC! WAKE UP!
I would almost certainly have purchased at least one or two of the core books in hardback by now if it were possible to get legal PDFs for them. (Better if you got a free PDF with the hardback, which most companies do nowadays.)