I'm glad you created this thread @AndyTravis - it's interesting because the problem of creating new songs must be one that haunts most bands - the one thing I've wanted for years was some kind of writing partnership and I guess we all feel we'd like that because we've all got our limitations and get stuck or run out of ideas or steam. There is a load of good advice and ideas in this thread that's why I had it in mind for a while to come back and go through it and read everything again - I liked a lot of comments first time through and liked a few more this time round.
The drummer sounds great so I'd focus on trying to work with him and I think you'll just have to try and accept the limitations and lack of useful feedback and engagement from the others - there are plenty of decent musicians and singers who just aren't interested, able or willing to get into songwriting - it's often not a simple or straightforward thing to do - it's difficult. You probably stop at some point because you aren't sure how best (or whether) to proceed and this is where you could just try and work out what input of feedback you want from the others - sometimes it helps to narrow down the problem for them. Do you just want the singer to write some words or even just work out a melody. I'm think it's hard to be too definite about rating fragments of songs - even with a few words - I've found it can take a very small change, a spark of imagination, to save something that seems to be going nowhere; those sparks often come through persistence imho.
I have a lot of unfinished songs where I have a verse, maybe 2 and maybe even the bare bones of a chorus - I'm good at starting things - OK on the words, melody, singing, finding chords but I'm not good at creating great rhythms or riffs or at finishing things. Most of the time I have no idea what a song might be about - I make up words and chords by improvising them both at the same time - I get a few more chords then add a few more words with a melody and this prompts a few more chords, the structure starts to evolve - it's all very ad-hoc - I never write all the music or all the words first. My closest musician friend of nearly 19 years now is completely different - he composes and records all the music for one song (often has the melody completely worked out too) then frets (he says) over the lyrics for weeks but then seems to write them relatively quickly - he doesn't do what i do and flit from one new song to another when I run out of ideas for one song. We both have our limitations but overall, he is far more successful than I am - I had hoped we would manage to work together on his or my songs but it's never happened - I'm confident sitting down with a guitar and blank page and I just don't think he would feel comfortable putting himself on the spot to work that way yet he's a good musician, singer, songwriter - we are just different. I send him fragments as I go along wondering if he has much to say - I'm open to suggestions; he sends me songs that are completely finished and really he is not open to any feedback at all but all credit to him - he gets the job done - I'm an admirer even if I think some of his songs could be improved with a bit of feedback earlier on in the process.
So - the conclusion I've come to - and I think this is where you might be too - is that, if I want a supportive songwriting partnership - I need to find the right person or people to work with or just try and do the whole thing myself - could you and the drummer put your own band together or is there enough of what you want and need in the rest of the band for you to stick with it?
If the singer has only contributed a few songs in a a couple of years I think you can just forget about trying to involve him. Does your band play many covers? Does the singer suggest any? If that's more in line with his background singing covers - maybe he can focus on that, finding interesting, possibly little known songs, or thinking about ways to bring something new to old songs - I liked Noel Gallagher's version of Help - using a lot more minor chords to suit the lyrics better - even a mashup.
What's happened anyway - any progress or how you are going to work with your band to satisfy your want to create more original songs? You sounded a bit frustrated you just hadn't had any help or feedback from the band that was that useful. The limitations of the lockdown aren't likely to be helping - I've found my friend most helpful when we've been in the same room together and I have his full attention on a fragment I've started on - he's nowhere near as engaged when I've emailed over an mp3.
Keep us posted!