For me, it's so totally and utterly simple.
You cannot generate a loud atmosphere when the vast majority of your vocal fans are split into two separate sections. That is, Union FS and that end of the Kop, and L/K Blocks.
I sit almost bang on the halfway line, so I can hear both sections. Often you will have both blocks singing different songs at the same time, both of which sound quiet from where I am.
On the very rare occasions both sections are singing the same thing, they are usually at least 2 seconds out of time with each other. This invariably makes the song fizzle out.
If you could find a way to bring these fans together (and others who feel they can't be vocal where they are), perhaps in a dedicated standing section, or by swapping the Kop and the Family Stand, you'd solve the problem overnight.
The club isn't bothered though.
On last night, the atmosphere was worse than usual. I think weekday night games generally do have a worse atmosphere. Not having WYS before kick off maybe didn't help, as did the fact Sunderland really took the game to us.
Even the Sunderland fans, who travelled in large numbers, were rarely loud. I expected them to really embarrass us but they didn't.