>
The internet as a whole is probably one of the least regulated markets> What stops smaller search engines from competing?
At the risk of sounding condescending - the IP protection legislation [1]. Please bear with me as I'm not about to make a value judgement here, merely point out the mechanics.
Right now Google holds a vast trove of data - indexed web content, users' search history and behavior, and algorithms to generate search results based on the aforementioned. No competitor may use that trove to improve their products or services unless Google gives them explicit permission by licensing. This is enforced by the government based on Copyright Clause and Berne Convention and other; the enforcement is pretty quick and can involve swift disconnection from the network, forfeiture of internet domains, etc.
I'm generally against blanket removal of IP protections.[2]
Having said that, consider a thought experiment: data being free as in free beer, and whomever manages to grab it, could use it. Both static data, and use of APIs. Be it copy of Google's indexes and algorithms, or perusing results of direct queries from Google to further their own search results. Employees free to exfiltrate data and code and start up competitors to Google. This would give many a competitor a leg up in the battle to catch up and perhaps overtake.
What one can do currently is either go DDG way, by improving incrementally on Bing and other contracted sources while remaining at the mercy of their whim, or do what Bing did - try to sneak a bit of the crown jewels here and there [3]. The later didn't do Microsoft much good.
Re-emphasizing, I'm not advocating abolition of IP regulation here, nor making value judgement; merely pointing out that there's regulation in place - and it gets acted upon swiftly and to pretty strong effects.
--
[1] just as well as the network effects, brand loyalty, access to VC, and other aspects discussed upthread
[2] I want the protections to run for meaningfully shorter periods of time
[3] https://www.wired.com/2011/02/bing-copies-google/