Why is there less action anime every season? Why aren't there anime like Ninja Scroll anymore? Anime like Attack on Titan or One Punch Man came out and they were huge hits. But then each season, anime studios do more romance and slice of life animes.  With shows like Bleach, Naruto and One Piece, why are studios so hesitant to make an action anime series?
Looking at the MAL Lists for 2017 by their definition of action genre:


Winter
49 of 243 anime released were action genre (20.1%). 
Spring was 43 of 237 (18.1%). 
Summer was 37 of 249 (14.9%). 
Fall is 36 of 206 (17.5%).


2016


Winter was 52 of 252 (20.1)%.
Spring was 51 of 235 (21.7%).
Summer was 56 of 241 (23.2%).
Fall was 61 of 278 (21.9%).


2015


Winter was 58 of 227 (25.6%).
Spring was 55 of 222 (24.7%).
Summer was 54 of 249 (21.6%).
Fall was 64 of 265 (24.2%).


Lets jump to 2010


Winter was 42 of 177 (23.7%).
Spring was 37 of 171 (21.6%).
Summer was 41 of 171 (24%).
Fall was 50 of 181 (27.6%).


And another jump to 2005


Winter was 24 of 138 (17.4%).
Spring was 27 of 131 (20.6%).
Summer was 34 of 147 (23.1%).
Fall was 29 of 154 (18.8%).


Final jump to 2000


Winter was 14 of 88 (15.6%).
Spring was 15 of 87 (17.2%).
Summer was 15 of 103 (14.6%).
Fall was 21 of 107 (19.6%).


From looking at these lists - and I'm probably going to look into the time between 2005 and 2015 in more detail when I'm not at work, it seems more like we got an upsurge of about 5-10% in action anime that's either taken a slight blip now, or has trended back towards year 2000 levels. 

One of the main things to happen between 2000 and 2005 is the anime releases of both Naruto and Bleach. Their take off and massive surge in popularity both in the east and west could have sparked an anime boom in getting action manga (and just action ideas) to production; however this is just conjecture without sources to back this up.

It would be interesting to know if this was a trend followed when Dragonball  first went to anime too. 

Just in general though, we've seen a large increase in the amount of anime being released. When the most popular (and safest bet) action anime stems from the adaptations of shows from Shonen Jump and other shonen manga, who only have space for a certain number of different manga in their magazines, then it would follow that an increase in total manga should see a decrease in the percentage these manga adaptations take up.

If I get time I'll also look into whether I can find any stats on take-up of anime outside of the "teenage boy" demographic, and look to the success of the non-action genre releases (such as the stand out hits that came from the Slice of Life genre).