The reason for this comes down to price, cost per use, and overall usefulness. Now, I know some people don't care about price, but it really is kind of a big deal. UR Cyclops are going for absurd prices at the moment and you can get two Xavier for less than one Cyclops. Since two Xavier bring you to 1800% boost and one Cyclops brings you to 1000% there is very little reason to go the Cyclops route. In fact, two Cyclops only bring you to 2000% boost. Making it only slightly better than Xavier.
Now, cost per use also plays a role. Assuming you have 320 attack power, which would be a significant amount. You can attack 20x with Cyclops (we'll ignore the+5s for easy math). So lets say a total of 40000% in boost. With Xavier you can attack 22 (with 12pts to spare) times, once again ignore the +5s. This would be a total of 39600% in boost. With higher stats Cyclops is the clear winner here, but personally not by enough to warrant paying double.
The final kicker though is the overall usefulness. Ultra Rare Cyclops has a Degrade to opponents attack and defense of tactics alignment cards. I believe this is the worst skill out of any UR card in the game at the moment. Xavier has an attack boost to tactics alignment, the best buff for offensive tactics decks.
Overall, I wouldn't even risk picking up an UR Cyclops for fear of having to try to get rid of it after the event is over. Xavier is hands down the best X-Men Raider Card.
You've been warned about buying Cyclops!