There's another issue you've missed - this isn't comparing like for like - a bomb goes off somewhere else, it's often clearly part of an on going struggle, and normally is claimed by one side or the other. Everyone knows who's done it. It's covered in the news and that's about that. There's a police investigation, but that's rarely interesting enough for an update on the news until they have a development like catching someone.
But in this case, it wasn't clear straight away who did it and why. It's been going on for a few days now, with new developments, shootings, man hunt, then one suspect dying, a large section of a large city being locked down and people told to stay in their homes etc - it's not just the case they report the bomb and then that's it - it's giving new developments over and over, the story is changing each news bulletin, not a case of reporting the same thing in slightly different words. (which gets old quickly). They aren't giving lots of extra column inches to the bomb that went off on Monday, they are now covering what's happened since Monday, what's happening today.
Add into this, it's taking place in a country with very well development media coverage, in a major city - UK news agencies can piggy back on local news coverage, they will have footage, and new footage, at good intervals (eg the BBC last night was covering what CNN had said). It's taking place in a city with a lot of private indivduals on twitter, facebook etc and they are directly contacting news agencies with updates, it's easy to get the latest development and to contact people effected.