I watched this happen, it was death in slow motion. Sony never gave the Vita the resources it needed.
2011-2012 - Vita launches with 25 games.
E3 - 2012 - Sony skips the Vita at E3 and instead devotes 30 minutes to "Wonderbook". When asked why they skipped their newly launched console, Sony explains that there's only so much time during a keynote. The Wonderbook would not last the season.
E3 - 2013 - Vita games are shown, but they are chiefly indie games that are available on other platforms like Spelunky. Tearaway, the stand out exclusive title, would eventually sell only 14,000 copies and be ported to PS4.
E3 - 2014 - Sony skips the Vita at E3 and instead devotes 30 minutes to talk about the Powers TV show, a show which, at the time, had not even been cast and had nothing to actually show. Both the show and the video service it's on would soon be cancelled.
2014 - Sony announces first party games are scaling back, hard to scale back from something that was barely there in the first place, and would focus primarily on Indie and 3rd party development.
2015 - Sony admits publicly that AAA development on the Vita has stopped at all internal Sony studios.
2018 - Physical game production stops.
2019 - Vita hardware production stops.