I am not an expert on the original IRA (and will gladly defer to folks that are more knowledgeable than me); or even much of one on later iterations; but I felt compelled to point out that the devastating Omagh bombing you linked to was neither perpetrated in the 1970s or 1980s (it happened in 1998), and was not an act of the Provisional IRA (the IRA group most people think of when the think of the "Troubles" of the 70s and 80s).

The Provisional IRA had decided upon a ceasefire in 1997, and the "Real IRA" was a splinter group of members who did not support it. The Real IRA were the perpetrators of the Omagh bombing.

The Real IRA was more concerned with impacting and disrupting the economy of Northern Ireland, likely the reason for the bombing in a retail sector. The Provisional IRA that preceded them had been more focused on a specific urban guerrilla war against the British (and various groups that supported the British).

The majority of the casualties of the actions of the Provisional IRA were members of the military. Another ~10 percent were PIRA members who were killed by their own bombs. Around 35% were civilians. These figures include politicians and judges that were killed, but other civilians were reprisal killings for the deaths of Catholics killed by Loyalist paramilitary members. In general, the car bombings targeted the Royal Ulster constabulary, the British military, or economic targets. The bombing that you linked wasn't actually perpetrated by the PIRA, but by a splinter group named the Real IRA. They were unhappy with the peace agreement that the PIRA had agreed to.

It's worth pointing out that the Omagh bombing wasn't about purposely killing as many civilians as possible. From your own link:

Three days after the attack, the RIRA claimed responsibility and apologised for the attack.

If they intended to kill as many civilians as possible with this attack they wouldn't have reacted the way that they did to killing so many civilians. Obviously they did and that's on them.

The membership of the RIRA at the time was almost entirely former members of the PIRA, who knew indiscriminately bombing civilians would not gain them popular support or "legitimacy". I recommend the "IRA Green Book" (full copy) which is a short book that was issued to new IRA members, the one in my link is a combination of the 1950's and 1970's versions (the only ones to surface publicly so far). It paints a clear picture of the motivation and rationale behind the bombings.

There's two parts from this book in particular I'd like to highlight for the purposes of this conversation:

The enemy through our own fault or default is the one we create ourselves through our personal conduct and through our collective conduct of the struggle: the wee woman whose gate or back door gets pulled off its hinges by a volunteer evading arrest and who doesn't get an apology as soon as possible afterwards or more preferably has the damage repaired by one of our supporters; the family and neighbours of a criminal or informer who has been punished without their being informed why. In brief our personal conduct as well as our conduct of our Republican activities must be aimed at if not enhancing support, at least not creating enemies unnecessarily.

And little later it says:

By now it is clear that our task is not only to kill as many enemy personnel as possible but of equal importance to create support which will carry us not only through a war of liberation which could last another decade but which will support us pas t the 'Brits Out' stage to the ultimate aim of a Democratic Socialist Republic.

At the very least I think it's clear that the Omagh bombing didn't go as the RIRA intended. The attack was a contradiction of everything that would have motivated their members and they would have fully known that blowing up a pregnant woman and a busload of tourists from the Republic would only weaken them and their "struggle".