Sony stopped caring 4 months after release. Vita was released in February 2012 in West. E3 2012 for Vita was pathetic. It had less screen time than their PlayStation Mobile initiative with HTC. Only two games were shown: A logo for Call of Duty Vita and 3 to 4 screenshots for AC Vita.
To be clear, portable games were never highlighted at Sony's E3 showing, except for the very first PSP show in 2004. The best you ever got was a title announcement or two and a sizzle reel. They've had years with both great and bad portable slates that they never talked about, just showed clips of and then had out on the floor to try. Handheld titles don't show as well, the audience that watches conferences isn't as into those games as AAA console titles, investors and journalists tend to be of the same mindset as the watchers, and the games themselves tend to be developed on a different timeline and so are less done at showtime.
Portable games are also rarely a highlight of Nintendo's showings, and when they were, it was always a
bad sign that Nintendo's console line-up was weak.
I do feel this had a big hand in it. All of the console's flagship games were overshadowed by something else. Uncharted released months after Uncharted 3. Killzone Mercenary released just before Shadow Fall. Assassin's Creed and Call of Duty were alongside their console counterparts.
To a point, I agree, but do remember that both Sony and Nintendo had success in the past piggy-backing portable games with high-profile console games. It worked in cases on PSP and GB (I can't think of times when Nintendo had both Cube/Wii and DS titles together, they might have already been aware that the trend was not working like it used to.) The logic was that there were not just one but two games in a high-profile franchise to go check out (it saved on marketing too,) and sometime they even tied in together with link features. Gamers might have changed with their tentpole focus, and games have gotten longer and more involving (especially with online play,) crowding out whatever interest there was in dual-platform brand launches (didn't help that portable games were becoming "console-quality", which made them less special even if they added to story canon.)