When you act without experience or reaction, you just get a performance. It feels very stilted way of speaking with odd punctuations on seemingly random words that makes it very unnatural. Sometimes when a voice actor has to do a "voice", they're so focused on making sure that voice sounds consistent that they forget to make it sound natural. This is the vocal equivalent of always being on-model. When people speak, they are capable of changing up their voice in a multitude of ways while still sounding like themselves. Nobody ever speaks in the same tone and cadence the entire time. Tom Kenny can make Spongebob sound excited, mad, bored, depressed, or confused and he doesn't NEED to make sure Spongebob is squeaky-sounding the whole time-- but it DOES still sound like Spongebob no matter what he's saying.

The Breaking Bad fake dub video is already a perfect compare-and-contrast example to illustrate bad acting vs. good acting.

https://youtu.be/4kyxZI1UCKM?si=UuyHxnczPP0bkCnr

https://youtu.be/ci8dIpNcyEY?si=NL9E1FwoPU1oqzAu