2nd generation British guy here from a (liberal) Muslim immigrant family, although I'm not religious at all FYI.

My family talk about these kinds of events a lot at home, and we all find them horrific. I think there are a few reasons why it might appear that we condemn them so timidly:

1. My family often feel that these kinds of stories ostacrise them further from the community that they're trying to integrate into. Therefore, they don't exactly go out of their way to bring these issues up with non-Muslims. In fact, I remember my mum not wanting me to get public transport the day after a terror attack from the fear of someone taking their anger out on me. This was probably a bit of an overreaction on her end, but it's not unheard of

2. I feel like there's a bit of a divide between the non-Muslim perception of what the Muslim community is, and what our own perception is. We don't view these extremists as part of "our community".

3. At least in the UK, the Muslim community is very isolated. When was the last time that you heard a Muslim leader's opinion on anything?

4. It's a bit hypocritical to expect Muslims to apologise for the small number of extremists, but not expect — say US citizens to apologise for their government's own killing of civilians in Muslim countries. The majority of sane Muslims don't hold ordinary US citizens responsible for these killings (even if you support the government that is behind them) so we don't feel like we have responsibility either.

5. As you said, the media may simply not be reporting on Muslim condemnations of attacks. Here's a massive list of Muslim authorities/scholars condemning terror attacks.

I've got no love for Islam, and believe that your point does hold some truth. All a Mosque what would have to do is put up a banner outside condemning terrorism in the week following a terrorist attack. What do you think would an appropriate response from the Muslim community following the recent terrorist attacks?