You have to put Stradivari in context. He lived in Cremona, where the basic design of the violin, viola, and cello were created from the viol family by sometime in the mid 16th c. by Andreas Amati. The Amati family then continued to make violins, violas, and cellos. By the later 16th. c., the violin had emerged as an excellent instrument for the professional musician: it had a pretty wide range and treble voice , so excellent for playing melody, and was loud enough to play a concert for a large gathering, or be heard for a dance. It was also light and portable. That popularity among professional musicians created a lot of interest, and people began to compose for it. As the violin music scene grew in the mid 17th c., so did the number of Cremona builders, like the Rugeri and Bergonzi families. They and the Amatis trained other makers- like Stradivari , and Guarneri. When Stradivari began work on his own, finishing his apprenticeship circa 1660, he and other Cremona makers therefore had had the benefit of more than one hundred years of accumulated violin-making experience. And it's important to see the importance of the growing market for them: many compositions by Vivaldi, Telemann and other Baroque composers needed string orchestras, and it would become fashionable for a wealthy noble family, like the Esterhazys, to have their own ensemble. The nobility would be willing to pay for good instruments, Cremona violins, violas, cellos were prized, and so nobles would send their servants to Cremona to buy the instruments for their ensembles. Then the Cremona shops would be able to employ more workers to build more (and even better) instruments.
That Stradivari was perhaps more prized than other Cremona makers in his time can be gathered by the number of other contemporary builders who used his violin as a model, like Barak Norman, the most famous English Baroque maker, and Claude- François Villaume , the most famous French maker. He was not always the model: Joseph Hill would model his instruments on Niccolo Amati's, and Jacob Stainer in Austria probably learned from the Amatis but developed a somewhat different instrument. And Stradivari's reputation also was tied to his output. The Stradivari shop was productive. It would, according to some estimates, be able to make and sell something around 20 instruments a year, along with bows, etc . Stradivari lived to 93, and so it's thought somewhere around 1,100 instruments were made there. The more instruments got out, the more they were heard, and the more buyers knew his name. So, someone in England might have known the name Stradivari: fewer, for the same reason, would have known the name Guarneri.
And while there's no doubt that Stradivari's instruments were highly regarded, it was after his death in 1737 that his reputation was blown up very large. The market for fine violins grew even larger in the following century, as orchestras became larger and more common and ceased being the hobbies of the nobility. Unlike other Baroque instruments, violins , violas and cellos could be altered and modernized, and so demand for them continued. Their value also rose because they got into the hands of virtuosi, and were played very well. In the 19th c. they also became collector's items: because of Stradivari's's output, there were also Strads around to collect ( to use an analogy, it is possible to collect Picasso artwork because there's plenty of it, while it is impossible to find a Vermeer). So, you could say that Cremona instruments were highly valued at the height of the Baroque, Stradivari's perhaps more valued than others, but it was only in the collectors' craze after his death and the Romantic era that he became much, much more valued.
Heron-Allen, E. (2018). Violin-Making, as It Was and Is (Classic Reprint). Forgotten Books.