Why wouldn’t they? This technology is not a competitive advantage for their company, wouldn’t make sense for them to sell as a standalone product, and it helps their engineering department attract good talent.

Here's some community stats for Bloomberg open source projects

https://devboard.gitsense.com/bloomberg

For the 200 repos that they have made open source, they had over 6000 people contribute feedback and/or code. So in addition to attracting talent, they also get more testers and feedback.

Full Disclosure: This is my tool

If it gains wide adoption, then they've got a global community of people providing free software engineering for their messaging platform. Its a win-win.

Because they're not making money off of their queueing system, but what they build with it; to them it's a cog in their machine, and open sourcing it means others may adopt it and help them maintain and improve it.

They must not consider it a trade secret, so they can earn good will, generate public contributions, and advertise their brand by sharing it.

Hiring strategy--there are a ton of people who'll take a slightly lower salary if they can get a public record of their code commits.

Same reasons any company open sources their software