HELP I'M A CAT
If you mean someone that uses a character simultaneously in many RPs, I so agree- it's hard to really get into the mindset when they're in so many things! Though I can't say I get why a character can't have been in an RP before? Personally I incorporate previous RPs into their history, changing the history depending on the RP if for example it doesn't fit the theme-ing. But then again I think maybe you're thinking of only romance-focused RPs? Because if people RP many genres and don't fully focus on romance I think it's unlikely a character will have just fallen in love with every single character they've RPed with!Pre-made characters.
It can work in VERY specific cases, but 99% of the time they're the biggest turn-off ever.
I want unique, engaging, characters that belong to the world we make for them... not a recycled character you mash into every different scenario. It takes away so much of the charm for me to know that Billy-Bob Jr. has been madly in love with twenty different characters across a multitude of roleplays. It's almost like someone is looking for wish fulfillment and want to use me and whatever unique character I come up with to get there.
This is kind of nuanced because it does depend on the situation. Sometimes if it's a pre-made character that hasn't been used anywhere it can be really cool (ie. a character you came up with that fits into a specific unique world that you want to explore via a roleplay), but when it's just the same character across a billion different plots I can't help but get annoyed. Especially because characters like that tend to not have much (if any) room for character growth because it's all happened before.
Then again if you mean 1x1... I haven't done that in at least twelve years... xD I do know there's a -lot- of people that do mostly 1x1 (not nearly everyone of course!) that just want the romance stuff.