When you understand the causes of suffering and your own experiences with dukkha, you understand also that other people experience similar sufferings too.
Having compassion for your own suffering, it's hard to not extend that compassion to others who are suffering in their own way. Or so I find anyway. Unless they're a jerk - but even then, I'll try.
I won't go into discussion on 'limitless' or 'boundless' compassion here - I'm just referring to common concern for the sufferings and well-being of your fellow man.
Of such compassion, I do not see any vacuum within the Theravada tradition.
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"Whether I were to preach in brief, Sāriputta, or whether I were to preach in detail, Sāriputta, or whether I were to preach both in brief or in detail, Sāriputta, rare are those who understand." (A I 333, Sāriputtasutta)