I for one, don't have the time to pack many encounters into a session. Nor do I think making my players wait months to gain any kind of meaningful benefit from their adventuring careers, or weeks to recover their abilities, is particularly worthwhile.
My groups gain a sense of satisfaction out of watching their characters improve and gain new abilities. That's not universal, but I can't be alone in this.
Since gaining a level might not even necessarily give you more than hit points and a ribbon ability, based on the precise level and class, and gold quickly becomes useless unless I step in and give it a good use, having an adventuring "day" take 2-3 sessions, when I'm lucky to get my group together twice a month, just doesn't work.
So when I prepare encounters, I make sure the individual encounter is something they can handle, and I let them rest when it's logical for them to be able to do so. Even though some profess this makes the game "easy mode", I have seen characters die in sessions I run, and I even have a TPK (sort of) under my belt (black dragon fight in Forge of Fury, at a certain point I told the survivors that if they wanted to flee, I'd allow it, and end the adventure, rather than watch them get destroyed. It took a few minutes, but they ultimately decided to take my deal).
Now I'm not saying I'm some kind of gifted DM when it comes to making encounters- I've made mistakes, and I wish the DMG and Monster Manuals were more help to me, but they haven't been.
I need a certain amount of enemies to make an encounter challenging. I need enemies who have at least a 25% chance to hit the PC's. The published monsters don't always measure up.
This means I'm often forced to use higher level enemies, which means that bounded accuracy doesn't seem to be working either- what good is it that I can use 8 Bugbears if none of them can even hit the Fighter or the Cleric?
So the way I see it, the guidelines are useless to me. I know I'm not alone in this opinion. Further, the monster design and challenge rating rules are also mostly useless to me, since two encounters with the same experience point budget can have wildly different results, and that's before I even add things like terrain or other factors which can alter the difficulty.
Further, it seems WotC knows that these guidelines aren't worth the ink they're printed on, since they don't use them themselves!
So if they have no trust in this sort of thing, how can anyone else?