Justice League was a disappointment.

Nobody is saying money makes a good movie, in terms of box office expectations Justice League was a serious disappointment and struggled to make a profit; that is why there's been a recent reconstruction at Warner Bros. For crying out loud, it's the Justice League: Wonder Woman, Superman, Batman, The Flash, Aquaman, and Cyborg all together in a single movie and coming off of the heels of Wonder Woman's success the movie should've made more but it didn't and it lost to the third Thor movie think about that for a second. 

Your Transformers argument does not really work - The three MCU movies released in 2017 did pretty good critically and were quite liked by most movie goers whereas the Transformers films are in the "critics hate it, but audiences like it" category of the cinema marketplace. The most recent entry scored the lowest with critics and audiences and made way less profit than prior entries. Now if you were talking about Iron Fist and Inhumans, which are not made by Marvel's film division but are in the MCU technically speaking, then you might have a point in terms of reception, but neither of them were designed to be movies they were for TV.