I don't pretend to know the long term sustainable measures we should take, but I view as cancelling all social gatherings, working from home, restricting non-essential travel etc as good measures that we can take now to help slow down the spread.
The key point though is that our governments
do have to think of the long term sustainability of these measures. And things like school closures, travel bans, avoiding social situations and elderly people avoiding crowds
aren't sustainable for as long as it will take for a vaccine to become available. They have to weigh up what impact different measures will have, when they will come to an end, what will happen at that point in terms of any surge in cases and what their plan at that point will be given an attempt to re-introduce those measures will inevitably have less buy-in and be less effective. They also have to take into account what measures they can and can't enforce given they're not a totalitarian regime like China.
Ireland and the UK have (according to Ireland's CMO) taken different approaches to the crisis from the start, as now reflected in the different measures being taken. Ireland's approach has also been praised by the WHO, notably unlike the UK's.
Even with those differences though the two countries (and multiple others) still agree on the same basic principles. Namely that measures should only be introduced at the point they will be most effective, as per data modelling that draws on the individual circumstances of each country. They also agree that introducing these measures too early will hinder efforts to control the virus
because they are only sustainable for a certain period of time.
So when you ask "why haven't they introduced X already?", it's because their data modelling based on the reality of what they actually can and can't do has told them that it isn't the optimum time to do so yet. Simple as that. I'm not sure what you'd expect our countries to do beyond following that modelling, especially given "be like China" and "sustain unsustainable measures" aren't really options.