Actually, I've been thinking of how this may have come about, because I remember PlayStation fanboys being very different during the PS1/PS2 years. Back then they were a little bit smug but didn't defend the console as fiercely as what we're seeing right now. I think the most rabid Sony fanboys right now are in the same headspace Nintendo fanboys were in during the N64 and Gamecube years, despite the PS4's position in the industry right now.
During the PS1/PS2 heyday I don't remember first party Sony games getting hyped up all that much except maybe Gran Turismo. Sure the main mascot platformers were a big deal but people didn't pin the hopes and dreams of PlayStation on their backs. PlayStation was still the only place you could get Tekken, Metal Gear, Final Fantasy, etc. PlayStation fans were more chill in their smugness back then. What changed was probably PS3. All those Japanese third party exclusives dried up. PlayStation initially wasn't getting games like BioShock or Oblivion. When Tekken and Final Fantasy finally did come they showed up on Xbox too. PlayStation fans needed games on which to justify their $600. Sony first party games became one supposed messiah after another: Uncharted, Resistance, KillZone 2.
Even though Sony's back on top Sony fans seem to still be in that insecure mode. They still seem to need The Order 1886, Uncharted 4, and Horizon to legitimize themselves. Maybe it's that Sony kinda started off the PS4's lifespan with a pumped up marketing campaign that has pushed "PlayStation" as an identity more than ever before.
You don't really hear that much from Xbox fanboys these days though. I wonder why we don't hear as many people viciously defending Halo, Gears, and Forza.