Why did Proto-Dravidian words not begin with consonant clusters?

In Proto-Dravidian, words were strictly structured around monosyllabic roots, which consisted of specific combinations of vowels and consonants. The language did not permit consonant clusters at the beginning of words because its phonological system was defined by these simple root structures, where a vowel could stand alone or be preceded or followed by a single consonant.1

While Proto-Dravidian words did not begin with consonant clusters (such as kr- or pr-), these features emerged later in certain branches of the language family. For instance, in South-Central Dravidian languages, sound changes involving the movement of apical consonants from the middle of a word to the initial position eventually resulted in the development of word-initial consonant clusters.12