Multiple vs Single ProtoBuff

I am having a discussion with my fellow architects,

We have 3K line big ProtoBuf, Which has lets say 10 different feature specific message definitions.

Question: why cant we have 10 different proto file than having in one signle file. so each module has its own protofile.

I want to know whats the merit of splitting. I believe irrespective of splitting we can achieve the same.

In single proto file, each modules will only implement only their feature specific needs. so what we are trying to save by splitting.