Google's robots.txt does not tell the full story.
For example, if you include a User-Agent header and put certain strings in it, e.g., "curl/7.47", you will be blocked.
echo -e 'GET /search?q=robots.txt HTTP/1.1\r\nHost: www.google.com\r\nUser-Agent: curl/7.47\r\nConnection: close\r\n\r\n' |socat -,ignoreeof ssl:www.google.com,verify=0
The problem with the robots.txt "standard", e.g., ones like Google's with no "crawl-delay" directives, is that it does not define what is a "robot". The query above is obviously not a "robot", but Google, with all it resources, still treats as such.
Google probably does more (abusive) scraping than any other entity. Web scraping is in their DNA. It is in their web pages, too.
curl https://www.google.com/search/static/gs/animal/m05py0.html|grep scrape