For me, it's that Timeranger feels more like the production style in 90s Sentai than in 2000s Sentai. Gaoranger pretty much changed everything regarding how Super Sentai seasons were approached.
It's nothing rational, just how I feel about Timeranger in particular. Virtually everything made after Gaoranger-- even Boukenger and Shinkenger-- honestly reminds me more of Gaoranger than almost anything before it.
Zyuranger also to me felt like it marked another major stylistic shift. You can sort of compare Jetman to the shows of the 80s, but everything after Zyuranger feels just a world away from the 80s style.
On some level I'm expecting Goseiger to introduce the next decade's big changes in production style. It feels like a very "different" season from the promo materials.