Being a “traditionalist Muslim” is a reactionary term. The term had to be coined in order to make the necessary distinction against “modernist” and “reformist Muslim.”
The defining feature of a traditionalist is respect for the intellect of past Muslims and a skepticism in the validity of modern exceptionalism. The modernist, in contrast, is skeptical of the intellect of past Muslims and a firm believer in modern exceptionalism.
In other words, modernists believe we live in a unique time and that that necessitates practicing Islam in a way that it has never been practiced before. Modernists also tend to believe that, in modern times, we have unique knowledge that past Muslims were not privy to, and that knowledge licenses us to practice Islam in a way that it has never been practiced before.
The traditionalist, on the other hand, finds this reasoning not only unconvincing but even irrational. What is so unique about modern times that merits the adoption of unprecedented beliefs and practices? Over the past 1400 years, we are still the same species with the same needs and basic mental makeup, the same tendencies, the same weaknesses. Which is not to say that Islamic law does not accommodate certain kinds of changes and variation across time and place. But our times are not exceptional and unique enough to even begin to justify some of the things modernists call for.
Traditionalists also respect the intellect and spiritual insight of the collective body of Muslim scholarship over the past 1400 years. If there are beliefs and practices that the vast majority of, if not all, scholars upheld, that in itself is evidence of the validity and soundness of those beliefs/practices. The community does not agree on error. What makes us so special, what unique intellectual capacity do we have to go against the tide of historical unanimity?