For wired internet, I suspect that a lot of people are paying for much faster connections than they actually need. As you note, e-mail, streaming video, playing online games, and browsing generally don't need a lot of speed. Latency and packet loss are far more important.
25 Mbit/s is fine for streaming one 4K UHD video with surround sound.
It is mainly just large downloads where speed matters. Downloading a new game, or a big update to a game you have, or a major OS upgrade, will usually take longer on a slower connection. (Not always, because the server might not be fast enough. Not everyone pays the bandwidth costs to allow their download servers to support a bazillion simultaneous gigabit/s downloads).
When I dropped cable TV/phone and went internet only, I decided to cut my speed from 600 Mbit/s ($90/month plan) to 100 Mbit/s ($55/month) to see if it was good enough. (If not, it could be raised easily just by placing an order on Comcast's website. No need to even interact with a human--they only make you interact with a human if you are trying to do something that will lower your bill).
That was 6 months ago, and it is still sitting at 100 Mbit/s. I almost never notice that it is slower than it once was. Most large downloads I do are things I download in the background while doing other things, and then get to sometime later. For most of them, all the change from 600 to 100 did was mean that the gap between the download finishing and my getting around to wanting the data is smaller.
One other important consideration is uploading. My old 600 plan had something like 25 Mbit/s upload. My 100 plan only has 7 Mbit/s upload. That sometimes is noticeable, such as when I need to upload a file to a server for work, then ssh to the server to do something there with the file.