Why do exs…

[Eastwestt]

…continue to stay in touch, message you etc even when they’re with someone new?

No kids, no marriage. Ego boost? Safety net? Hoping for a reconciliation?

I've had this from a few of my exes (women, as I'm a man) and I have no clue either.
Usually it's just a 'how are you, hope you're doing well' type message - perhaps it's because they feel bad for how the relationship ended (some were unfaithful) and felt guilty because they'd moved on.

Maybe they're after a shag, or maybe they're just chatty - who knows!

Yes it could be any of those. It depends on the person. Some of them want to get info on how you're doing and stop you from moving on. Usually whilst they are. With men it's very rare to be for no reason/friendship.

I'd go no contact personally. At least for a while.

Just block?

Not had this, block?

Because they like the ego boost ooh look she text me back she clearly isn't over me or ooh look she has blocked me she clearly isn't over me doesn't matter what you do they can still make it look good for them

You're the safety net for whatever their needs are at that time.
Validation, ego boost, a channel for their arousal, emotional safety, unconditional love, ... Whatever it is they need, they know you've given it to them before so they reach out when they need a new dose.

Ego boost or hoovering when they’re single.

The last guy I dated was always randomly messaging me the ‘I miss you’ BS. Until he met someone else then told mutual friends I was the one chasing him 🙄

Nonsense. I'm in touch with several x's, they're great people and still great friends!