One thing folks in the US don't realize is that Mercedes is master in upmarket salesmanship in the US. We only see their higher end models. Mercedes apparently are quite popular as fleet vehicles in Europe and sell some very stripped versions of what are typically fully optioned out models in the US. Cab fleets and police departments don't buy they for the image I expect they get great fleet pricing. Considering the SEE is sold as a road going tractor I don't think fit and finish was an important factor.
Well, erm... *most* folks. I've been all around this planet over the course of my life. Cop cars & taxis, hard to say whether BMW or Mercedes has the upper hand, but those German fleets aren't the cheapest... but they do last forever enough longer to cost-justify their initial purchase. American politics is why American manufacturers have the upper hand here -- nobody's congressional district makes Mercedes bus/truck motors eh? Although they increasingly build lower-end BMW, VW, and Mercedes products here, or in Mexico or Brazil. The rest of the world is "the same but different" compared to here. If I were less lazy, I'd google up the most-popular truck motor on the planet, and it would probably be the Mercedes or Volvo, not the Cummins.
That Mercedes motor in our FLUs, is the bog-standard fleet motor everywhere else on Earth outside America (where Freightliner is owned by Daimler who sold Dodge to Fiat anyways, heh). It isn't a tractor motor, it's a bus/lorry motor. Last time I was in SF after my Dad died, was to sell the house so I stayed in a hotel on Fisherman's Wharf and couldn't sleep in past 6am due to all the tour buses lined up outside idling due to the Girl Scout convention staying there. I'd guesstimate that 1/2 of those buses were Mercedes motors, the other 1/2 Volvo, in this day and age. I didn't spot any GMCs, which are the awesome used American buses to buy for motorhome conversions, which I almost pulled the trigger on before I bought the (better for my purposes) '77 GMC motorhome.
It isn't the fleet pricing, so much as the reliability/longevity of the German products which put them ahead of everyone else from America to Japan to South Korea, etc. One thing I surely love about my Mogs are those motors -- pricey to service with experts few & far between HERE, but everywhere else on the planet, OM352 isn't an unfamiliar term -- like saying "Cummins" in America. The most popular taxi cab in China is their knockoff of the Toyota Crown, i.e. late 80's - early 90's Camry, fwiw.
Ditch the crappy fuel hoses, replace some metric fittings with SAE, and the OM352 is as reliable as a Cummins, here, and the cost of genuine, certified parts is actually a wash (as opposed to parts cost on a Mercedes sedan vs. a Camry, or Honda Accord) on the Mercedes motor (that's as much of an oddball in the US as a Cummins is outside the US) compared to Fleetguard parts for my Dodges.
I'm a big fan of motors, more so than the vehicles they come in. Honda & VW fuel-injected four-bangers... BMW, Mercedes, and Cummins straight-sixes... the 455 Olds LBC in my motorhome... the boxer-twin BMW motorcycle engine. When I get a Vanagon Syncro, I'll be getting one with the Subaru boxer-six upgrade, which is a bog-standard car motor here in snow country. It doesn't really matter how many of what vehicle I have from one year to the next, all my motors are on a very short list of reliable gear.
It pains me to say I'd rather buy a fleet of BMW or Mercedes taxi-cabs these days (Uber/Lyft aside), than Chevy. Daddy had a '55 Chevy back when I was born (with a cobra on the hood, no less), and right through to the modern day, the '55 Chevy is still a bog-standard taxi cab all over America because we used to know how to do what the Germans and Japanese and South Koreans are known for, while we've dropped down into a dead heat with the British and Italians for building crap. Don't even get me started!!!