[Baeocystin]

Not an accident. Energy. Rome as a meta-organism was limited by available energy- trees weren't enough, and denudation of forests was already a limiting factor. Meanwhile, Britain had plentiful coal in easily-accessible abundance. No point in developing steam and a theory of thermodynamics when you can't use the results.

[sideshowb]

I thought denudation of forest was a limiting factor in the UK too, indeed a motivating factor for https://en.m.wikipedia.org/wiki/Abraham_Darby_I

[Baeocystin]

It absolutely was. It has been everywhere! The difference being that the UK had coal to fill the need.

[wbl]

Italy does have some coal and Rome at one point had the coal seams of the UK.

[Baeocystin]

Yup. The Romans in Britain did use coal for their hypocausts. But too far away, too little, too late for the Empire at large.