I started with Maniac and then Zak when I was arround 8 or 9 years old on a C64.
I played both, the english and the german version, but can´t longer remember if I already had the german version for C64 or later on my Amiga only. I liked both. I also played Space Quest, Kings Quest and Police Quest back then.
I liked the LFG Games way more. But I wanted to solve the others too.
I can still remember how I sat there every day with the english school book of my three years older sister to figure out what was going on or in case of sierra, what I had to type.
When english started in fifth grade in school, I was already quite good 
But as soon as I had the german versions, I loved them. finaly I understood everything.
For me it has always been the mix of a good story, beeing challenged with that puzzles and OF COURSE the humor of the old LFG/LA Adventures. From Maniac to Monkey 2 and later. I loved DOTT and Sam&Max too. But DOTT a little more then Sam´n´Max. It was more “crazy”.
I can´t tell how often I played this games in my life untill now. Way too much or not enough. Who knows.
Why germans like them, I don´t know. Only that all of my closest friends loved them and a few still do.
Pirating? Was a big game back then. I had hundreds of copied disks on C64 and on Amiga and I went to the store every week to buy new empty disks.
I didn´t own Maniac or Zak at first. A friend of mine got Zak and we copied it (damn brown code site with black letters… needed some tries to copy that in a shop
) Much later I bought my own Maniac for Amiga and still have the disks. I copied Monkey Island at some point and that game was it for me. Pirates! Beeing one! Nothing before that was like that. I got sucked into the story, the game, the amiga - for hours. When part two came out I bought it immediately… 120DM… fxxxing much money for a child. I couldn´t wait. But I loved it too.
Indy, Loom, over the time I had them all some copied, some bought at first glance like Indy 4 and Monkey 2.
Much later I bought collection boxes with all the games combined in it.
Did I bring new answers to the threads main question why germans like adventures so much? No.
But I wanted to share.

My Hardware back then over the years, in this order, some at the same time:
Commodore plus 4 with datasette (broke really fast), C64, Amiga 1000, Amiga 2000, Amiga 500, 386 SX20, 368 DX40, 468 DX 100 and so on…
My Uncle was a crazy computer guy and worked with them, I got almost erverything until the Amiga 2000 from him or through is influence on my parents. 
And no, we weren´t near to rich. Nope. My mom worked at home and my dad was craftsman