The original Silent Hill games were created by an internal group within Konami called Team Silent. This team was formed by underperforming Konami staff to work on a Resident Evil competitor that Konami higher-ups wanted to underperform and give them a chance to fire said underperforming staff. Instead, they struck gold with SH1.
Team Silent suddenly had a level of fame to themselves, but they were still Konami's red-headed stepchild. 2-4 were similarly successful, with 2 being the high point of the series.
After SH3, key staff started to depart from Konami. By the time the 5th game, Homecoming, came out, much of the original team had been replaced with those more aligned with Konami bigwigs that wanted to turn the series into a moneymaker instead of the quiet success it was built as.
An example of this is the Silent Hill HD Collection for PS3 and X360. The 'remaster' of SH2 and 3 was anything but. They had to make these remasters with incomplete codebases, no original staff to question, even some of the original voice acting was missing because Konami straight-up deleted the original source code.
There are those that say that SH never recovered from the gutting of Team Silent, and they tend to get louder with each entry into the series. Sometimes they have valid points, but not always.