Java is one of the most popular programming languages for years. Many enterprise companies still heavily use Java programming language and have legacy applications written in Java. But when it comes to AWS Lambda (or serverless in general), it has some challenges and cold start is the most infamous one. This is one of the challenges they face when they want to migrate to AWS Lambda as rewritten all the applications with another programming language like Node.js, Python or Go may not be feasible for them.
Lambda Sources and Thundra Layers ~ A match made in Serverless