The term Spam Can was orignated in the US in the early post WWII years as a mild put-down of new-style aluminum structured aircraft, generally having nose wheels and focused on the mass market. Comparing that type of aircraft with a round engined tube and rag classic, it's easy to see why those with a more romantic soul weren't attracted to them. Regardless of that, C172s and the like were in reality the most utilitarian planes to date and they sold like crazy for that reason... 'spam can' or not.
The term is still commonly used among US 'antiquers' today to describe newer aluminium structured planes.