@icedquinn His work was not really suppressed, just too difficult to understand to make sense of anything out of it for 90% of the physicists. Freeman Dyson also remarked that he was also being too modest about his E&M theory, and only described it as the new theory that he prefers (in comparison to the old Newtonian "molecular vortex" based theory) at that time. Dyson said if he promoted his own view harder, it may have accelerated the progress by 20 years. http://www.damtp.cam.ac.uk/user/tong/em/dyson.pdf
Also, Quaternion was the standard tool but Maxwell himself didn't use it in particular in the Treatise, what the book did contain was 10-20+ equations for a bunch of different electromagnetic things known at that time, and they were all in Cartesian coordinates for each X/Y/Z polarization. Other people already used quaternions in E&M, including reanalyzing Maxwell, but many physicists found quaternions were completely devoided of physics intuition and it was likely a reason why Maxwell's theory was so difficult to understand.
Heaviside reanalyzed the theory in term of vector calculus and simplified into 2 for E&M waves and is crucial for making the theory understandable today. Heaviside told his readers about this life story in one book about E&M:
More than a third part of a century ago, in the library of an ancient town, a youth might have been seen tasting the sweets of knowledge to see how he liked them. He was of somewhat unprepossessing appearance, carrying on his brow the heavy scowl that the "mostly-fools" consider to mark a scoundrel. In his father's house were not many books, so it was like a journey into strange lands to go book-tasting. Some books were poison; theology and metaphysics in particular they were shut up with a bang. But scientific works were better; there was some sense in seeking the laws of God by observation and experiment, and by reasoning founded thereon. Some very big books bearing stupendous names, such as Newton, Laplace, and so on, attracted his attention. On examination, he concluded that he could understand them if he tried, though the limited capacity of his head made their study undesirable. But what was Quaternions ? An extraordinary name! Three books ; two very big volumes called Elements, and a smaller fat one called Lectures. What could quaternions be? He took those books home and tried to find out. He succeeded after some trouble, but found some of the properties of vectors professedly proved were wholly incomprehensible. How could the square of a vector be negative? And Hamilton was so positive about it. After the deepest research, the youth gave it up, and returned the books. He then died, and was never seen again.