To answer M0YNGs question.
The reasons are a mix of "that is how people use it", and "technology was then made to work that way because that is how people use it."
DSL is a split of bandwidth for up/down in that way.
FTTP is shared. Downlink can send consecutive packets to any combination of users, no gaps. Uplink has to "slot in", or even ask for a slot, and uplink in that slot to not clash with other users on shared medium. So uplink is slower.
I hope that helps.
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^RevK