It's not a weight weenie thing. In fact from my search it actually usually weighs slightly more. Most of what I'm reading suggests that it's actually more reliable in adverse conditions than mechanical, or at worst that it's roughly equal but different.

Having ridden DI2 for over 10 years, in the Canadian winter, with salted roads, I have to believe you’ve never used/maintained/serviced an electronic drivetrain.

The mechanical parts will fail as equally quickly - in the same places - if not maintained.

I’ve not yet had an electronics failure on my three electronic drivetrains. Mechanical bits will wear out as per usual.

Until the recent influx of low-cost electronic group sets, the ones on sale from SRAM and Shimano were high-end enough that they were/are incredibly reliable with the exception of the first generation external Di2 Dura Ace battery which had a poorly designed mount that would indeed cause issues over time. The internal battery remedied that issue.