I think there are a few reasons why 1911's can be perceived to have reliability issues.
1) There are so many manufacturers at so many different price points in so very many calibers. Some are quality manufacturers and others are not, and price itself is not a very reliable indicator of which is which. With such a large number of manufacturers, quality and tolerance issues are inevitable. Any complex device requiring detailed manufacturing is subject to quality variations.
This has also been the case with other designs. When S&W more or less copied the Glock design to make the Sigma, the S&W-version had some teething pains. Is the Glock design poor? Is S&W not a quality manufacturer? Not in my opinion, but S&W learning curve to make a reliable Sigma was high.
There is no pistol design factory-chambered in as many calibers, and some of those calibers have not been chambered in enough 1911's to get all of the bugs resolved.
2) The shorter barrel length 1911's are more difficult to make reliable due to the short slide length and decreased slide mass. Getting the whole spring rate and slide speed equation balanced is a trick. In addition, the barrel tilting angle changes with barrel length which adds another variable to the system. The 5" versions are more reliable than the 4.25" versions, and the 4.25" versions are more reliable than the shorter versions. This is also true of other designs. Shorter Glocks are not as reliable as full-size Glocks.
3) Magazines. The Achilles heel of every auto-pistol. Personally I have had very good experiences with Wilson-Rogers #47D and factory Colt magazines. I have seen a lot of junk magazines out there including "G.I." magazines which look like they were tossed in a tumbler with rocks.
4) Gunsmithing. A lot of people work on 1911's, and some of the work causes problems. This is compounded by the sheer number of after-market parts available. I once saw a 1911 go "full auto" after an errant trigger job. I have also seen hammers following slides. These are not the fault of the 1911 design or even the manufacturers (for the most part). Much of this happens after a 1911 has been sold.
5) The original design was made to feed ball ammo. As the ammo has become more complex, the 1911 has had to adapt to the ammo. There was a learning curve to do so. Some older pistol designs also had the same issue, such as the S&W 39. The difference is S&W has second-generation and third-generation pistols to distinguish improvements, and we still call all 1911's "1911's". I think the newer 1911's have proven to reliably feed many of the new ammo designs.
6) The extractor. Probably the weakest part of the design because it requires tension to be properly adjusted. I screwed up a few myself before I got Jack Weigand's tool. Having the right tool to do the job is important, and for too long, I did not have the right tool. I think the external pivoting extractors are an improvement on the original 1911 extractor, and I am putting my money where my mouth is with a Kimber U.S. Team Match II.
After trying a lot of pistol designs, I have settled on the 1911. Why? Because it works for me. Are there other designs that work? Absolutely. But not as well for my set of needs.