I've noticed that several gals log in and don't check their PMs. Now these are well-established major-league gals that I've seen before and have dates scheduled with - they know me and have seen me and have agreed to see me again. I'm just trying to make some adjustments... WTF?
I will admit that I don't usually log off even when I leave the computer - sometimes even when I go to bed I may still show up as online if I leave computer on.
I do get notified by email when I get a PM and since not always actually at computer I do try to answer as soon as I'm able, whether on my phone or on computer.
Just like all of us, providers are subject to over stimulation. Consider a provider has an email, a cell phone, a pm, and other means of contact. Active provider have an incentive to return messages received. If they don't, then it is likely a life event happened. Just go with the flow.