minecart speed is decreased when somebody not ride minecart
Linked issues
Comments 2
I believe this might be intentional. The way that minecart travel was changed in Seecret Friday 7 was that you had to propel yourself with a Minecart with Furnace to travel long distances faster. There was really no way at the time to automate moving long distances until Beta 1.5, when powered rails were added. Simply put, there was no way that a minecart with chest would be allowed to move indefinitely, or even far distances, so the minecart has added momentum added into it when a mob or player is inside it, allowing for faster travel.
TL;DR; Notch made this an intentional part of minecarts early on in the game. This is not a bug.
Can confirm for 20w18a (macOS, singleplayer), I have made a small loop, which a minecart cannot complete, but with a player, it does so without a problem. It seems to be an actual bug as it is not listed on Minecraft wiki (source).