I find this term incredibly annoying, as it is applied so broadly as to have no meaning beyond being generally insulting.
It has a meaning here... you're talking about "undubbing", which in this case means the replacement of english audio in japanese-originated games with the original japanese audio. This means that the people who do this, and the people who enjoy it (yourself included since you're complaining about a lack of it) prefer the japanese audio to the english audio. Preferring japanese to english to the point that you'll take a language you understand and replace it with one you don't? Those are the actions of somebody who has a strong like for the japanese arts, to the point that it's reflected in their personal tastes and actions (even changing retail arts to suit their tastes). The common term for this type of person is a weeabo.
So it certainly does apply to this situation.
Anyways, PSPs have traditionally been easier to hack and play ISOs from than the Wii. I'm not talking now, but over the course of their lives. Pure-ISO loading is relatively new to the Wii, earlier models (well, earlier drives to be precise) would play burnt discs just fine and that was the norm. People didn't feel like burning disc after disc after disc to check the progress of their undubbing or hacking attempts. Compare this to the PSP, which has
never played burnt discs, always loading ISOs from the memory stick. It also helps that the PSP's form of ISO loading has almost always been pure-ISO (ISO-9660 extended on a FAT/32 partition) and easily modified. Compare this to WBFS and such that the Wii used to use, where you needed special tools to modify the custom filesystem for loading backups. This means much faster, easier, and cheaper testing, which is conducive to modding games... so overall it's been easier to mod PSP games than Wii games.
In addition, the PSP's had a lot more JRPG and such releases than the Wii from what I see, which means a larger pool to pick from. Even if the ratio of both (percentage of officially-localized games undubbed) was the same, the fact that the PSP has a larger pool means that the number of undubbed games for it will be higher than the Wii.
So that's probably why. More games to pick from and an easier process.