It's just more complex. I worked on a project in the mid-late 90s that had a couple of hundred developers, building a system of maybe 150 db tables not incl. j

It's just more complex. I worked on a project in the mid-late 90s that had a couple of hundred developers, building a system of maybe 150 db tables not incl. join tables. 20 years later, I worked on a similar sized rails project, with a team of 5. A team of 100s now is going to build something vastly more complex and featured than similar teams before, with a consequential increase in the number of issues. Think of something like a code editor, or spreadsheet. This would be a major project in the 80s - now it's almost a homework assignment.