Niantic Labs CEO, John Hanke, posted an update on the company's Pokémon Go news page explaining why the company decided to block third-party developers from accesing the game's servers to create Pokémon tracking apps and websites:

We were delayed in [rolling out Pokémon Go to Latin America] due to aggressive efforts by third parties to access our servers outside of the Pokémon GO game client and our terms of service. We blocked some more of those attempts yesterday. Since there has been some public discussion about this, we wanted to shed some more light on why we did this and why these seemingly innocuous sites and apps actually hurt our ability to deliver the game to new and existing players.

Hanke also noted that the cost of allowing data scrapers access to their servers affected gameplay at all levels.

In addition to hampering our ability to bring Pokémon GO to new markets, dealing with this issue also has opportunity cost. Developers have to spend time controlling this problem vs. building new features. It's worth noting that some of the tools used to access servers to scrape data have also served as platforms for bots and cheating which negatively impact all Trainers. There is a range of motives here from blatant commercial ventures to enthusiastic fans but the negative impact on game resources is the same.

On a positive note, Niantic is "actively working on" fixing and returning the Nearby foot tracker to Pokémon Go. And, since they aren't spending so much time trying to combat server issues due to data scrapers, maybe they will actually have a chance to fix it soon.

I was a fan of Pokevision, myself, and was sad to see it shut down. But, I feel confident that the team at Niantic Labs made the decision to block data scrapers because of the negative affect it was having on gameplay and not just because they don't want people to cheat.