Ok, so you would be perfectly fine with waiting behind me in line in the drive-thru while I asked detailed questions about each and every menu item, had a discussion about it with my passengers, and then, after about 20 minutes or so, placing my order through the intercom? Then, when I got to the pay window, figuring out how to split the bill between me and the passengers, paying after about 5 minutes worth of calculating and counting money. Uh oh - then I decide the add something to my order and ask some more questions about menu items, and think about it for a bit and then place my order. Then we go through another 5 minutes of calculations and paying. And, finally, 30 minutes after I got to the menu board, I'm at the window to receive my food. I check each and every order as it comes out and discover that one of them is wrong - well, it was not ordered correctly so it needs to be changed. More questions about menu items and discussions ensue and another order is placed. More calculations and paying are done as the original calculations are rendered invalid due to the incorrect order. Now, it's aobut 45 minutes after I (and you!) arrived at the drive-thru and I finally have my food and you're finally getting yours. But you're ok with this because it was convenient for me.
Keep in mind that this is not a "pull to the side and wait for your large order" situation. Each of these steps required interaction with the workers.
I'm sort of with the OP. If you're going to go through the drive-thru, make it as quick as possible. You can order 14 happy meals but there shouldn't be special orders and modifications from standard.