Well ofcourse they do this to keep up their profits, they are a business after all.
But is it really that weird or unheard of that a company after some 10 years raises a few prices to get them more in line with their offerings at the other side of the pond?
And surely inflation won't be the biggest factor, but after 10 years you cannot fully discount it either, i feel that the biggest driving factor here is currency exchange though, when Blizzard set most of these prices Euro to Dollar was 1 to 1,25 to 1,30 now its 1 - 1,07 (last time i checked yesterday) which is a huge fall for the Euro compared to the Dollar. And since Blizzard counts in Dollars the last few years they have gotten alot less dollars for their euro's which hurt their margin i reckon. If you look at the financial statements you can also see that profit margins are dropping year after year, in 2012 Activision Blizzard had a turnover of around 4.5 billion dollar (hope i say it right) with a profit of 1.15 billion dollar, in 2016 they had a turnover of more than 6 billion dollar with a profit of around 900 million, thats a big decrease of profit margin in just 4 years.
If they would bump prices every year by these amounts, surely it would be unreasonable, but one price raise in 10 years, i personally don't think its unreasonable, i even expected it to happen alot earlier.
Tech companies like Samsung, Apple, Nvidia, Intel to name a few all bump prices nearly every year the last few years atleast in Europe (when ever the newest generation comes out) i find that a lot more unreasonable than this price raise.