Difference is a crawler paces the requests, respects robots.txt and rate limits, and doesn't typically invoke 50-100MB disk I/O per request.
Like I don't mind automated access to my search engine, I even offer a public API to the effect, that you can in fact hook into SearXNG. What I mind is when one jabroni with a botnet decides their search traffic is more important than everyone else's and grabs all the compute for himself via a sybil attack.
If you delegate queries to e.g. google or bing at that rate, you'll be ip blocked in a heartbeat.