Could be they’re working and planning to move in after work?
we were delayed by 4 hours because our solicitor “forgot” to tell the estate agent (or us) that everything had gone through (we had been forced to use that solicitor for the purchase and we refused to let them do the sale as SIL worked for a conveyancing solicitors firm and we wanted to use them, the firm we were forced to use were bloody awful and we weren’t impressed with them at all).
they could be moving from a long way away, so Ieft their old property at midday and have a 5 hour drive to get to their new property?
They might be unwell and unable to manage the move but have completed etc already and are staying with family/friends until well enough.
They might not have completed yet - your old neighbour may have moved out today as got a long journey, or going on holiday and won’t be there when completion happens
Their car or moving truck might have broken down en route
Moving from rented and have given themselves time to move slowly
Might have booked a cleaning or decorating service to come in before they get all their stuff in there
Could have bought intending to let it out
could have bought it as a second home - my parents bought their “retirement home” YEARS before they were ready to move out from where they were and it sat empty for a good 8-10 years before they were finally going to move in (although they did start to get bits of furniture in there, work done and go and sit up there for an odd afternoon during that time).
There’s likely millions of reasons when you think of all the things that could just delay someone every day. I find it interesting that your first thought was a funds issue - especially as the person moving out was likely relying on the money coming through to buy wherever they were moving to, so if the funds well through their inward purchase will have too!