I’m no expert, but there are a couple of ways languages tend to change in this way. The first is to reduce acoustical interference, in other words to take out sounds that seem (unconsciously) not to do much to the word. Think about how we say the word “talk” versus how we spell it. Verbally we mostly drop the ‘l’ but don’t lose a any ability to understand. The ‘l’ isn’t necessary to differentiate different words in most instances.
The second is the tendency to simplify anything that can be simplified (a kind of speaking laziness) known as the principle of least articulation effort. Think “knight”, which even as recently as Middle High German pronounced all the letters.
But neither holds always true. Sometimes languages just change for no apparent (or discernible reason), and not always to become easier to say. And languages also change because of outside influences - for example two language groups being in close contact for a long time (English and Danish in the Danelaw sections of England or English and French post 1066). These other two principles sometimes have the opposite effect (like English’s ridiculously inconsistent pronunciation rules around ‘ough’).
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