The last place I worked at will die because it will take them years to migrate from Oracle to postgres due to "technical debt" (the codebase is coupled with the database to a hilarious degree; business logic in triggers, huge plsql packages, plain sql queries in the java codebase, halfassed homerolled ORM). They're not getting as many new customers as they could because, for various reasons, the Oracle licensing terms are now unacceptable for the new customers they have been in contact with over the last two years.

That's the most concrete reason I can come up with why the technical debt will kill them, but there's plenty of vaguer reasons why it's been killing them for the past 5 years and will finish them off over the next 5. The attrition rate have been around 20% a year since I joined. For most of the time I worked there they compensated somewhat by hiring new people. Word has gotten around though, and they've run out of qualified candidates willing to work on their mess. Hell, we even had a couple of gifted hires leave after a month or two while shaking their heads.

My current workplaces main product is using the same tech, is the same size (loc) and has the same functionality of the other company, but serving a different market. They did the oracle to postgres migration in 2 months. 2 MAN months, one guy.

New workplace: 15ish developers, serving the same amount of customers, doing similar revenue, making stable releases every week

Old workplace: 80 developers at its peak, doing non-hotfix releases around every 3 months. Just a mess in every way. Mostly stemmed from the codebase and the architectural choices that had been made along the way.