Lawnmowers, Plug Up

Two questions burning a hole in mind this morning.

Why are mower mufflers a single, ineffective layer of inline baffling when it would be relatively cheap and easy to bring the motor's sound down by 30dB with an auto type muffler? Are manufacturers really that cheap? Even higher end mowers have the same loud output. There must be a reason, but I can't find an answer.

WTF is with the substitution "plug up" for "plug in"? Is it regional? The first place I ever heard it was at the Monday jazz jam at the Blue Room (before I got my house gig up the street at the Juke House). I assumed it was part of jazz culture, but since I've heard it all over. What is its etymology? Who uses it? How long can I stretch out this research to avoid doing any actual work?