If these films are just fluff, theny why are they so overlong?

Because Michael Bay doesn't know the meaning of the word "restraint". Think about it. This goes back to his stuff in the 90s.
His shortest movie BAD BOYS is still nearly 2 hours while the sequel is 147 minutes long! His worst offender PEARL HARBOR was 3 hours in length while THE ROCK and THE ISLAND were also both well over two hours long;oddly the exact same running time at 136 minutes. Even his smaller movies like PAIN&GAIN and 13 HOURS clock over two hours.

Whatever you are, be a good one.

I was surprised myself(to my detriment). I thought meh 90min I will survive, but after 40 minutes I was ready to leave which did not happen until 2.5 hours later.

I doubt mind long movies as long as they are entertaining. This movie sucked so bad and I got bored halfway through it so I walked out. I will never again waste my money and time on another Transformer movie. It left a sour taste in my mouth. I don't even wanna catch up on the previous installments.

This is the biggest mystery about these movies. These movies are BASED ON KIDS TOYS and are obviously aimed at kids, yet they have these ridiculously long running times of 150 minutes+ that practically put the younger members of the target audience to sleep. After 2 hours of this stuff your eyes begin to glaze over as you begin to lose track of what exploding robot flying at the screen is meant to be good and which is bad and in the end you just find yourself yawning "When the fuck is this shit ever going to end ?" The sequels are all at least 50 minutes too long and undoubtedly it was only the fix up job done by Steven Spielberg in the fist movie that made it coherent enough to watch, even if it to, was too long.

You are absolutely right

Film editing is pretty much dead now.

It's so everyone can stroke Michael Bay's ego and tell him "If it was just fluff it couldn't be so long"