[elnatro]

Why some Romance languages had the hard C sound lost before e and i?

[linguistics__]

Because of palatalization [0], a very common sound change.

0: https://en.wikipedia.org/wiki/Palatalization_(sound_change)

[retrac]

A similar process is currently ongoing in some English dialects with initial t/d. "Tuesday" and "choose day" are homophones for some British speakers. It may well morph into "shoes jay" within another century or two. Or not. Sound changes tend to follow patterns but they are not really predictable.

[BrandoElFollito]

Thank you, very interesting. Is this across the whole language, or rather localized to some areas (geographic or other).

Also as a French walking in the street and saying Tuesday and choose day loud in the street, I got a few curious stares :)

[elnatro]

Thanks for the insight!

[pmontra]

Only when written, of course.

In Italian the written letters ce and ci are pronounced with a soft c.

There are plenty of words with a hard c (a k) followed by an e or an i. Italian alphabet doesn't have a k character so those sounds are written as che and chi. That is, in Italian ch is the k sound. Most (all?) of the other languages of the area use ch for a soft c.