captchas means not a site was hack it's for website's security why would hacker place captcha on site.
Exactly, why would a hacker add a captcha when it would be in their interest to let more people access the site for data mining or phishing?
Blockchair always had one if you used TOR or you did multiple queries, even for VPNs, if you try to play around with their explorer (which has a ton of options, probably the best one around) it triggers one. I've never encountered a captcha on my normal ISP IP, but a lot of times on tor. If you use a free VPN that is easily abused and already has most of its IPs blacklisted no wonder it will be the same.