Well, I wouldn't say dropped as much as "never the plan in the first place".
Obviously WotC want a situation where you feel you need to pay for their products to play their content.
The cheapskate option was probably intended as a plan B if 5E didn't do well. Since it very early became clear it was a success, there's just no reason to continue supporting the "free tier" - WotC clearly understand they don't need those players (or, more likely, can wait until peer pressure forces them to open their wallets)