Putting the indra thing aside, it's about who cares about who most and Izuna was the only one madara really cared about. So it took him until his late 30's to awaken the mangekyo sharingan because his brother was still alive and well.
Sasuke witnessed his whole family died mother and father yet still didn't awaken MS until Itachi died.
Obito's mom and dad died and he didn't awaken MS until Rin died.
It all comes down to setting and emotional ties, and that person who you're close to is not dead yet, then it'll take longer for your MS to manifest.