Because the DLC changed the in-game pricing system of the Care Package. Pre-DLC you could do many runs in a row and sacrifice the (relatively) low cost of spending multiple Care Packages. Because they were cheap, it seemed acceptable to encourage people to always use it, since there was no reason not to, aside from having to grind for it a bit, but that felt very achievable, and reasonable to make it part of the speedrunning meta.
The DLC made it so that the Care Package would always cost half of your entire hoard of Kleinesbucks (thank you Exy for coining that), with a minimum of 30K. This makes it so that your reserves are now drained drastically faster, and the whole process of grinding and resetting is now not really as feasible since you run out much quicker, unlike previously where it cost a fixed amount. Because of that, it no longer seemed reasonable to expect everyone to compete with this enabled, so the rule was changed. But that change was not retroactively applied to base game, so there the rule still remains.
