IPv4 is a barrier to entry, so ISPs like it.
The article says "Then there’s the fact that some ISPs just don’t see it impacting their bottom line and so can’t be bothered."
Its actually worse than that.
One of the things you want in a business is a barrier to entry for would-be competitors, the higher the better. If there is no barrier to entry then competition will drive prices down to the point where you can barely make any money (as any Uber driver will tell you). Having a barrier to entry lets you raise prices to just below the point where competitors would find it profitable to buy in.
Exhaustion of IPv4 addresses makes it difficult to start up a new ISP; you can't just request a few nice big /16 blocks to get you started, you have to go out and buy a /8 here and a /8 there. Meanwhile existing ISPs are sitting pretty with their existing pools of IPv4 addresses. In fact the secondary market makes those an appreciating asset, something else that businesses like to have.
If IPv6 becomes widespread then this barrier to entry disappears and the existing pools of IPv4 become worthless. So it is in the ISPs interests to delay this evil day for as long as possible.