I think it was a compromise between achievability and limiting damage what made it to be accepted decades ago. It was unrealistic to ask to not reach 1.5ºC back

I think it was a compromise between achievability and limiting damage what made it to be accepted decades ago. It was unrealistic to ask to not reach 1.5ºC back then, but the increase should be as low as possible to avoid reaching tipping points and triggering positive feedback loops that could put things beyond our possibility of control. Things are not binary, we are talking about global average temperatures, not the temperature you reach some day or season in a region. So you have to deal with uncertainty and that with higher global average temperature you will have the smaller version of the loops, even if you didn't reach the budget yet. But when you surpass enough them, then you will have more players that are changing the climate, influencing each other, and things will change faster. And there the decimal resolution may lose its meaning, your range of confidence will be much wider.