Studebaker was a very interesting company, and made some great cars. Like many of the smaller "independent" car companies, they introduced many innovative designs. I have read many books and articles on the company, my thought from what I have read is that the downfall probably began after the war. Studebaker quickly brought out the first all new post-war car, the very modern design 1946 Studebakers, complete with modern 'three box' design (instead of fast back or semi fast back) and the striking wrap around rear window on the coupes... and they were a sensation, 'first by far with a post war car'. The problem was that there were material shortages that limited production, and that after four years of no new civilian cars, buyers would buy any car they could get, including the warmed over 1942 models that the other manufacturers were selling. By the late 40s, it was more of a buyers market, and GM, Ford, and Chrysler were out with brand new designs to attract buyers... and Studebaker had its warmed over 1946 models (though very nicely updated with the cool bullet nose for 1950-51, and with a small block V8 in 1951). All new designs were delayed to 1953, which were the beautiful Loewy designed cars. The coupes in particular were beautiful, but some say that the design wasn't as successful on the volume cars, the sedans and wagons. Then there was the GM/Ford price war for market share that badly hurt the independents, and as Nash merged with Hudson to create American Motors, Studebaker entered the far less successful marriage with the faltering Packard. Although Studebaker did some amazing updates on small budgets, the 1953 engineering and chassis soldiered on. Even the Lark was a shortened version of those models, and you could tell when getting in because they didn't get the 'step down' design that other companies had moved to that allowed them to keep up with the lower design trends. They got a reprieve with the Lark... but only for that couple of years before Corvair, Falcon, and Valiant came out. When they badly needed new product, they developed the Avanti, a very good sports car, but it cost more than expected and incurred delays as they fine tuned manufacturing. Ultimately, many question whether as a financial matter, the board decided it was simply more profitable to focus on other lines of business (including STP!). An interesting piece of trivia... Studebaker owned exclusive distribution rights for Mercedes Benz in the US in the late 50s and early 60s... a right that they had to sell to raise cash as the end was nearing. Many older Mercedes dealers, such as one near my home, started life as a Studebaker dealer!
There are several books about the company and its cars, one of my favorites that covers it in detail is 'More than they Promised' by Thomas Bonsall.