I always read this comment and and amazed how people here underestimate the complexity of running a large business with global reach and billions of dollars in transactions. Airbnb is in >100 countries and uses home grown payment system. Now imagine the number of currencies it needs to process and number of finance and tax laws that it needs to follow. Also, when you have traffic at Airbnb's scale, architecture and engineering becomes competitive advantage. Every millisecond of performance improvement or every last % of latency improvements lead to dollars. Finally, Airbnb is heavily regulated at the regional and city level. So I am assuming they require army of lawyers and ops people at these regions to comply. This is a start, and I haven't even touched the customer support side or defense against fraud and other malicious actors.
Look at hotels.com, which in many ways is comparable. It has around 1000 employees (one thousand). From wikipedia:
Hotels.com has 85 websites in 34 languages, and lists over 325,000 hotels in approximately 19,000 locations.
Going back to your comments, you could rephrase some of the earlier comments as: why on earth would you need millisecond performance improvements for a website/product listing rentals?
Hotels.com is part of Expedia group. Expedia has 25k employees.
Millisecond improvement is needed because travel is commodity and bounce rate is very high. If website doesn't load in time, visitors bounce off to other providers
