system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What makes internet faster or slower?

What makes internet speeds faster or slower? How do companies improve on internet speeds?
gpt
It’s really just a function of plumbing, though digital.   For example, the volume of cold water coming out of your bathroom faucet depends on the size of the spout on that faucet, the pipe from it through the house, the pipe from the house to the street and so on to the source.  It also depends in whether or not other faucets in the same house are on, and to a similar extent faucets in other houses in your neighbourhood. 

If you want more water in the shower, you can buy a bigger faucet, but will require larger pipes through the house to increase the flow.  Eventually, larger pipes in the house will exhaust the flow from the street and you will need those upgraded as well which requires the water company to invest. 

Internet is much the same. Each interface (faucet) has a size and if you increase the size at the edge (your house) eventually you will need upgrades in size all through the connections back to the source(s).

Internet providers are constantly adding capacity and chasing slowness that comes from imbalances in edge capacity versus core and changes in usage patterns (popular content sources). 

Now consider all your neighbours install high volume sprinkler systems and have big pools that need filling in the spring and you get an idea  of what IPTV and Netflix/Youtube etc have done to internet providers and how hard (expensive) it has become to ensure things are “flowing”. 

Just some rambling from your local digital plumber :)