"Many families subscribe to the newspaper."
Translation:Viele Familien abonnieren die Zeitung.
In short: because grammar.
‘Abonnieren’—unlike the English ‘to subscribe’—is a transitive verb in German, taking a direct object. ‘To subscribe to something’ = ‘etwas abonnieren’. Sometimes, the opposite happens too: English uses a direct object where German uses dative, for example: ‘I am following you’ = ‘ich folge dir’.
This, of course, is nothing compared to grammatical yoga required to turn ‘
I like it’ into ‘es gefällt
mir’. I say this just to illustrate that translating word for word (or complement phrase for complement phrase) often doesn't work, and while the grammars of the two languages are in many way analogous, the syntax required by certain constructions can often differ substantially.
Don't let it. It just takes a bit of time to get the perspective needed to recognise those assumptions you make about how all languages work based on how yours does. Once that's done, it's much easier to stop making those assumptions, and accept and absorb the new rules and ways of doing things in the target language.
I too found this difficult a few years ago. There aren't so many verbs which use dative so if you can just remember them and assume that most others are accusative. A very kind Duolingo user helped me by making up this story. The verbs in brackets are the common dative ones. A kitten was lost and missed (fehlen) it's mother. A girl helped (helfen ) it. The cat liked (gefallen) the girl so she followed (folgen)her home. The girl's mother asked who the cat belonged (gehören) to . The girl answered (antworten) "no one". The mother believed her (glauben). The girl served (dienen) the cat some fish. The kittten thanked (danken ) the girl. The mother allowed (erlauben) the girl to keep the kitten.
I think that it may help if you learn this along with the word. Lists might help, Maybe make a list of verbs that take the dative as you go along e.g. helfen + dative and as we see here, abonnieren + accusative. I don't think that we can necessarily rationalise in all instances. See @Ly_Lar's comment above.