Part of it is they are mixed in professional environments (studios) for professional environments (cinema).

Part of it is they can't mix for someone with a 10 year old tv using its built in speakers in a shared living room with street noise, 15 feet from the sofa and a brand new TV through a sound bar in a rural mansion 8 feet from the sofa, and someone using airpods over Bluetooth.

Plus people tend to listen to things at a volume similar to conversational level, but in a cinema you listen to things at a volume that would be considered impolite to your neighbors if you did it in an apartment block.

Finally, sound engineers are artists and dynamics (louder and quieter parts) are part of their craft. Actors are artists and their vocal performances also have dynamics.

A question to ask yourself is have you considered more actively participating in the sound delivery methods of your media? I'm not here to say "all people are watching TV wrong!" but I would ask if most people have even thought carefully about their sound delivery choices, their own EQ settings in their TV, how well tuned their environment is for active listening, and if they just need to turn their volume up?

I appreciate not everyone can blaze the sound on max — but if you do have to sacrifice some volume, maybe part of that tradeoff is clarity of dialogue?