How come all of the characters that have returned and most of the new characters only appear for a few episodes before departing again?

So far it's happened with.
Sonia.
Stacey.
Deano.
Jane.
Stan
Aunt Babe.
Lee.

It's almost as if they are only signed up for a few episodes before they get full time contracts.

Stacey and Jane both have other acting obligations, the others appear less frequently because it's how the storyline rolls...

To be truthful I liked the way Sonia returned because they just blended her in nicely.
I do agree about the other though.

I've noticed that as well. It is a bit weird. Maybe the idea behind it is to steadily introduce these characters rather than chucking them right into the thick of things, but I have to admit I'm finding it slightly tedious now. The only one that's worked well is Sonia, as hers felt fairly seamless. The others have all been strangely anti-climactic.

Yeah Sonia's worked very well because when she found out that Carol had cancer she didn't drop her whole life and return to Walford. It's been very realistic I must admit.

Yeah I've enjoyed her return, also. Shame Martin hasn't come back but to be fair the storyline is working without him.

Probably to make them more realistic? It was a bit of a cliche that characters would just turn up out of the blue and decide to live in Walford again where presumably terrible stuff had happened to them or where there was people they didn't wanna see.

For instance, I still find it a bit ridiculous that Sharon decided to stay.

Stan knew he wasn't welcome in Walford and he was perfectly happy where he was so it would have been stupid for him to immediately move to the square. He has been integrated pretty well.

Aunt Babe hadn't seen any of the Carters in years so her slow integration is logical as well. She isn't about to up and move because of a few people that she rarely saw.

Dean doesn't want to see Shirley and considering she is centre stage atm, it is logical he ain't sticking around.

Lee is in the Army, as said both stacey and jane actors have commitments and Sonia has been integrated perfectly IMO. I love the fact she doesn't live on the square but is still a regular.