No, this is definitely a Discord thing. I've been in and out of all kinds of RP servers on Discord. And it's pretty much expected that you are going to reply quickly. The "Looking for RP" channels are filled with people just looking for a right here, right now kind of thing. I've been told many times on Discord groups that my multi-paragraph, once a day-thrice a week style/availability really won't jive with the rest of the server. I've also been told that I write "too much", and that I should go "write a book" from different Discord RPers. I've never been told that on a forum site.
It isn't "expected" on Discord. Some
people on Discord expect it, but it isn't some kind of unspoken rule. I understand that this thread is all about posting
mostly irrational preferences for a medium of role-play that has total user control, but let's not start spreading misinformation. It would be like saying message board role-playing expects multi-paragraph replies and if you aren't the most "literate" of writers, then you need not apply to try.
From my personal experience, I can say that Discord role-plays have been absolutely no different than forum role-plays in length and frequency of posting. I still write around 1k to 2k character posts on average, and receive replies matching or exceeding, as well as shorter. It isn't the platform, but rather the people you are playing with.
People that have this real fucking weird concept in their heads that Discord promotes faster posting and the forums promote slower posting. At best it's slower, because you have to click like once or twice to read the message and then a second or third time to respond. However, that does not stop you from posting many times a day on BMR. You could even just keep a tab open on your PM and pretty much get the same experience as using Discord when it comes to posting feel-- except you won't have to deal with the pesky character limit on BMR. I have seen people on this message board expect multiple replies a day, a single reply a day, a few replies a week, a single reply a week, and very rarely even a single reply a month. It's almost like Discord and Message Boards are just tools to facilitate social interactions, and don't have any hard rules on just how they are utilized for those purposes. You type into the box and hit enter.
I've used both Discord and BMR. I prefer Discord in some ways, because I like using servers for organizing things. I can keep character profiles handy, and easily separate out sections for images, music and OoC chat without having to rely on multiple PMs. It's all personal preference, and very few of these preferences are rooted in some kind of insane hard fact.
This next part is a bit unrelated.
Most of people's problems with role-playing comes from shit inside their own head. They're too impatient, too picky, have unpopular desires, or just not talented in a way that draws their partners in. Another huge factor is what they want to play and how they present themselves. Guess what, guys, if you're looking for a lotta smut role-plays and present yourself on the forum as cool sex guy in a suit or bubbly slut, then you're gonna get the kind of people that are looking for quick, smutty, shallow role-plays.
You're advertising
instant gratification, so that's what you're going to find. Even if you don't intend to, that's what you're signaling to people who are looking for partners on this forum. It just so happens that the type of people that like to role-play off site are often the same types that are looking for this instant gratification. They want to get you on a platform where they have more control and don't have to really answer to anyone. It's why this site has always had a problem with policing role-plays offsite and has various policies on it over the years. Luckily Discord is a platform where you have complete control over who you talk to and who can even send you a friend request. You can even block people in servers, at which point interacting with them is entirely on you.
If you have a bad time on Discord, then that is likely on your shoulders. If you have a bad time on this website, then that is likely on your shoulders. There are always exceptions, but let's not pretend like everyone here is the exception.