This isn't speculation. I have no idea what happened!
Madrid is about 2000' elevation.
It was hot- 30C.
They must have been heavy. c. 175 pax + fuel for a long sector.
( Could have been unlucky with pax weight as they were prob using standard weights.)
Wind was flukey. could eaily have been still air or even a tailwind.
Everyone knows the 'Mad Dog' is powerful, but 'on one', in the above conditions, surely it will need very careful handling.
Even if only a 'straightforward' EFATO or Fire on t/o this could have been really challenging and might even have left them with an a/c that wouldn't- or would hardly climb- alright, that IS speculation.
I pray for the families of those who are dead.
A tragedy.