TL/DR: it's about readability and clarity of unfamiliar code. One problem of large codebases is that they tend to be team efforts. Given a a sufficiently large

TL/DR: it's about readability and clarity of unfamiliar code. One problem of large codebases is that they tend to be team efforts. Given a a sufficiently large and flexible language, each team member will find their own style and idioms for their code. This creates the subtle problem that team members are unfamiliar with each other's styles and when they touch the same pieces of code, they each extend the subset of used language features by whatever is required for their favorite idioms. Eventually, the resulting code gets too elaborate for its own good and maintainability goes down. A boring, simplified language ideally constrains the team to use more or less the same patterns and idioms and this side-steps the problem.