Picture a wide net hanging behind a slow boat and dragging along the bottom of the sea. It is not aimed at one fish. It covers a whole stretch of water and brings up whatever was in the way. That takes hours, and it is heavy work. English then lends the same picture to searching: you drag through a whole pile of notes or files, slowly, and see what comes up.
From the word’s history
Wiktionary records trawl as a 16th-century borrowing from Dutch tragelen, to pull with a towline, from Middle Dutch traghel, a dragnet, and treats it as root-cognate with English drag. The idea of pulling something along is in the word from the start.
Wiktionary 記載 trawl 大約十六世紀從荷蘭文 tragelen（用拖繩拉）借進英文，更早的 Middle Dutch traghel 意思是「拖網」，可能來自拉丁文 tragula，並和英文 drag 同源。「拖著走」這個動作從字源就在裡面，所以核心畫面不是後人套上去的。
Wiktionary entry for trawl (kaikki extract supplied in this packet, source_ref kaikki:3f6f69a190036ae4:625847295)
登入就可以看每一支怎麼連回核心畫面。