Short answer is because they've set their DNS TTL to 5 minutes: https://mxtoolbox.com/SuperTool.aspx?action=a%3anews.ycombinator.com&run=toolpage https://mxtool

Short answer is because they've set their DNS TTL to 5 minutes: https://mxtoolbox.com/SuperTool.aspx?action=a%3anews.ycombinator.com&run=toolpage https://mxtoolbox.com/SuperTool.aspx?action=a%3anews.ycombin... As for why, you'd have to ask them. It could be to allow for relatively quick DNS failover in the case of an outage. Or if using a proxy like Cloudflare, that provider could prefer short DNS TTLs to have flexibility in their routing.