As a guitar/bass player? I used to have nice thick ones. Then I got lazy... And only played the guitar (or bass) when I needed to lay down a track. And there are plenty of other things that go in to tracking as you know. Now unfortunately, I have the fingertips of a safe cracker :-( So now when I get around to needing to track a guitar? I have to play it for weeks first. This is why the terrorists hate us, this is a true first world problem. 

I have the same thing sometimes. I have a family of 5 and can't always get down in the studio to practice. Luckily my job keeps them in somewhat rough shape, but not like they were when I was playing 4-5 hours a day. Whose idea was it to grow up?

It feels "good?" When you're on you're game? I've never been a great guitarist? But I've been good? 
 
When you pick it up and feel like a hack, it's disheartening... 
 
I'll rock on the tune I'm getting ready to record and will get it nailed ;-) But the whole, "used to be able to play effortlessly? Vs the whole, "DAMN! I NEED TO PRACTICE THIS SHIZ!!??"  It's well understood by those whom it is well understood by.
 
CCR - Green River... "Classic Rock." My favorite genera. 
 
"Well, take me back down where cool water flow, yeh. 
Let me remember things I love. 
Stoppin' at the log where catfish bite, 
Walkin' along the river road at night, 
Barefoot girls dancin' in the moonlight. "

As the forum podiatrist, I'd ponder that, although barefoot girls are spectacular, they, too, are apt to get callouses.
 
I'm getting lazier than ever I'm afraid.  'Not cranking new songs ... just polishing old ones.  Yup, No carpel tunnel, hardly a callous anywhere.  'Better get to work.

Found a secret...
 
...my venerable pawnshop Fender acoustic, with the stiff, mile high action.
 
After chuffing around on that for about a week, my tips get hard as rock and lightning fast!
 
Fortunately, it has the same width neck and string spacing as my SG.

I used to have rock hard callouses but after months of totally neglecting my guitar in favor of the keyboard, they've all but disappeared. Yesterday I restrung my Telecaster and got right back into it. Today my fingertips are on the verge of blistering. Wish I'd taken it easier. 

One of my favorite ways of re-callousing is to break out the twelve string acoustic for a few days. Rips my fingers to shreds at first but gets them in shape very nicely.

I know the feeling all too well.
Use it or loose it.
It's expensive (not monetarily) coming back.

I'm trying to play a little (at least a few mins?) each night. I think we all should. We are musicians? We're guitarists? We've spent many thousands on our guitars? Don't let your meat loaf... "Work it." Even if it's only for a few minutes? Play that damn guitar.

It's a big problem, and not just the callouses thing, but the whole already long round robin process of doing a song where you might not get back to a given thing for a month or more, exacerbated by having to do it in stolen extra moments. It means you can never really be as good as you should at any of it. It's the curse of the auteur I guess. If you choose to do it all yourself you have to accept the limitations that come with the control.
 
What I typically do is, as I'm doing my 'get the brain to turn off' time before I go to sleep, sometimes I'll put on a documentary or well known movie, and just sit on the bed with an acoustic and just do mindless exercises, playing finger style, so that I get maximum exercise and fingertip hardening, without having to invest too much concentration in it. And acoustic definitely does the most damage.