Title says it all. I am puzzled why Orion will be traveling faster than Apollo.
The premise of the question is questionable. According to Apollo By The Numbers, the maximum reentry velocity among all Apollo missions was achieved by Apollo 10, which peaked at 36397 ft/sec. For all missions, the reentry velocity was just above 36000 ft/sec or 24545 mph.
This flight test will demonstrate the performance of the SLS rocket on its maiden flight and gather engineering data throughout the journey before Orion returns on a high-speed Earth reentry at speeds of more than 25,000 mph. The high-speed lunar velocity reentry is the top mission priority and a necessary test of Orion’s heat shield performance as it enters Earth’s atmosphere...
25000 mph is 36667 ft/sec, so that would be a faster re-entry than any of the Apollo missions.
The return trajectory targets a high speed atmospheric entry on the order of 36,000 ft/s (11 km/s), suitable for demonstrating the performance and effectiveness of the Orion Thermal Protection System (TPS) heat shield, as well as relevant environments prior to the first crewed launch of the system.
But also here the reentry speed is in the same order of magnitude as those for the Apollo mission, not necessarily higher. So there seems to be some uncertainty.
Both resources mentioned that the higher reentry speed is necessary to for testing of the heat shield. The second paper mentions (on page 3) that the last burn of Orion is named "Return Powered Flyby", which to me sounds a bit like "floor it and see how fast we can go back".
We'll find out in a few weeks how fast Orion actually reentered.
Edit (13 May 2023):
The NASA page on Artemis-I Mission Facts section has been updated and now* states:
Re-entry speed: 24,581 mph (Mach 32)
This seems oddly specific to be an estimate, but I couldn't find a paper to substantiate this number. At 24581 mph or 36052 ft/sec (39559 km/h) Artemis-I's reentry speed would be slightly slower than Apollo.
*) The archive.org capture around the time I posted the original answer shows 24500 mph for re-entry speed.