Sometimes you start writing a play because you have some ideas about what you want to say, but the more you write, the more you realize that three unfortunate things are happening:
A) The characters all sound alike.
B) The characters all sound like you.
C) Everyone talks a lot, but no one wants anything.
While there is no easy fix to this, if you are bold and willing to hack up your text with a machete, there is a way forward.
1. Transplant your characters to an adversarial environment.
If you are writing a play that takes place in a library, Place your charachters on Mars, or in a desert, or in a maze, or anywhere that at least gives them external forces to fight against. It need not make any sense why they are there. They need not spend much time wondering about that. They are there, and they must get out.
2. Have a well-known political or pop culture figure walk into the play with a strong need for something from your characters. (This was the favorite advice of one of my college playwrighting profs. "Where is Thomas Jefferson? Where is Courtney Love?" he would ask. They never walked into my plays, but they often walked into Carter Bays' plays, and he went on to create How I Met Your Mother, so there you go. Sometimes it helps.
3. Put The Money Where The Mouth Is. If your charaters have been talking about artistic expression vs. commercial success, find a way to put their ideas to the test. Maybe they are in an art contest having this discussion. Maybe they aren't people at all but brushstrokes on a canvas having this discussion, trying to negotiate the ethics of moving how they wish vs. where the brush pushes them. Have your characters rob a bank.
4. Get a Job. Give your characters something physical and observable to do, like blowing up 500 balloons, or stacking and unstacking chairs, or serve food in a busy restaurant or... As we learned in improv, often it's very interesting to have an action unrelated to the conversation at hand.
Obviously, all of these require some new dialogue, stage directions, and possibly characters, but the good news is that you can keep your favorite monologues and dialogue exchanges; you just need to write in around them to avoid the "sitting and talking" trap. Do any of these tips fundamentally solve the problem of the play? Not really, but they will alleviate some of the difficulty and will result in a more theatrical play. (and as a former high school playwrighting competition judge, I was always thrilled to read plays that didn't involve teenagers or old ladies. Doesn't mean that the teens and grannies never won--but they did take up the lion's share of entries and it was exciting to read anything that wasn't locked around suburban, white, teen characters (and/or their gramms.)
This kind of playwrighting crisis happens to me a lot, by the way. I call it "sticking the skeleton back into the pile of flesh and muscle." It's about as easy as it sounds, but it always results in a better play.