Price elasticity of demand (=sensitivity to price changes). If the seller is afraid that higher prices will significantly impact sales (people won't buy the product or buy alternatives), it might accept a lower margin in order to maintain the volume.
Also market competition can be a factor: if competitors are not raising prices (or by smaller amounts), you might lose market share.
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?
Had the some doubts for our first hire - he wanted to work 4 days a week. He seemed committed and enthusiastic about our mission, so we went ahead.
Best choice we ever made: any doubt about commitment, passion, etc were blown away after a few weeks. He is now a cornerstone of our team. He still works 4 days a week. Now several key team members work 2.5 to 4 days a week, and we're doing great.
Looking back: I should have asked myself: what is better, working 1 day a week more or passion and a good technical fit?
Also market competition can be a factor: if competitors are not raising prices (or by smaller amounts), you might lose market share.