Why is it difficult to prove that Uralic languages are related to more distant language families?

Proving that Uralic languages are related to more distant language families is difficult primarily because of the significant linguistic changes that have occurred over the 7,000 to 10,000 years since the existence of Proto-Uralic.

These changes have resulted in the loss of many ancestral features, leaving scholars with relatively little evidence to support claims of deeper genetic connections. Because linguistic change is cumulative, the further back in time one attempts to reconstruct, the more difficult it becomes to distinguish between genuine cognates—words derived from a common ancestor—and chance resemblances or borrowings.123

While various hypotheses have been proposed, such as the Ural-Altaic grouping or the broader Nostratic hypothesis, these remain highly controversial. Most linguists require systematic evidence in phonology, vocabulary, and grammar to establish a genetic relationship, and the lack of ancient written records for many Uralic languages makes meeting these rigorous scientific standards a significant challenge.1243