In an attempt to haul this thread back on-track ...
Bitter disappearing? It is, but that started with the swing to gassy keg in the 1960/70s. I've been through this discussion before (it was probably
@Northern_Brewer putting things in perspective back then too, like his post above). "Bitter" hasn't so much "disappeared" as got "rebranded" into a multiple of "descriptive" terms. "Golden", "Amber", you name it ...
Here's a piccie of one (two!) of my "Golden" Ales (the ones I mentioned earlier).
View attachment 75840
Not actually a "Golden" but an attempt to replicate 1901 Boddington's AK. And AK was the Victorian precursor to 20th century "Bitter" ("Bitter" existed back then but was strong, around the SG 1.060 mark, and often termed "XK"). But the colour! Okay, it is a Boddington's recipe and they never got out of the habit of making it pale. But although crystal malt had been created back then, very little made it to "Bitters" ("AK" or "XK").
Dark coloured Bitters, now more often called "Amber Ales", didn't really surface until much later in the 20th century (as for dark "Mild", well search my posts for "Hancock's 1898 XX"). The colour in that AK comes from Invert Sugar No.2 which might disappoint some folk expecting more colour from No.2 Invert. (Wait to you see the colour of that Hancock XX mild ale! That used No.3 Invert).
No worry then that the disappearance of "Bitter" is accelerating. It's all in a name.
Credits to Ron Pattinson for digging up the recipes I use and the history, which I probably, inadvertently, massacre.