Ubisoft does not have enough new games releasing that's in good enough state to justify 7.99 per month let along 17.99 per month. I bet there are terms and trickery if people tried to do 17.99 and play games like new Prince of Persia and Avatar and then unsub. (that's my cynical side coming out, but it's ubisoft. )
Or, for ubisoft, you wait a couple month and then boom, big sale for the game released 1~2 months ago.
They gone viral and try to use their viral power to push as much to gain the capitals back. Yes it's not healthy and it could all go south really quickly if they don't manage it well. Viral go up and boom quickly but to sustain it is hard. You need actual good game loop and mechanics to keep player coming back for content drip.(assuming not live service game.)