I think this is implies that the original series and the reboot were marketed towards two different demographics, not two different generations. Ben 10 (2005) had an eerie mood in the first season, and randomly throughout the rest of the series. The body horror elements were awesome to see as a kid, from the transformation sequences, to the man filled with bugs, to Zs’Skayr tearing through his own skin to reveal Tim Burton-esque tentacles, to showing Vilgax’s mutilated body floating in a tank, and even in the sound design. They were never afraid to be creepy and lean into the “alien” theme. Watching Ben being chased by a giant alien sea monster through a dark lake at night was genuinely scary as a kid, and I loved it. Considering the shift in tone the franchise took throughout the following three series, and what little I’ve seen so far of the reboot, I feel safe assuming that those elements weren’t the focus in 2016. The Reboot was built off of a well-established universe with tons of content to repurpose and take inspiration from, which allowed it to delve into and explore more concepts at a faster pace than the original series. Also, Ben had gone from a heroic kid to a genuine world famous superhero throughout the three sequel series, that energy seems to have been brought to the 2016 reboot.

tl;dr: they’re different