The main reason for the aforementioned browsers not using libcurl is mostly historical, as it simply didn't exist back when they were created. (The newest of them is links, first released in 1999 - and according to the curl website, the first libcurl release with a proper interface was in 2000.)
w3m even uses its own regex engine for search, because there was no free regex engine with Japanese support the author could've used back then.
w3m even uses its own regex engine for search, because there was no free regex engine with Japanese support the author could've used back then.