It started out being not as “pythonic” as pytorch and so people flocked over to pytorch. Many new papers and models are implemented in pytorch and very few see the point in converting them to tensorflow since many of these models just run on desktops or servers. That said, both frameworks have their ups and downs. I myself have started with keras when it first got integrated into tensorflow and haven’t really wanted to use pytorch because it’s limited in being brought to web/mobile apps.