Because that would be «о́чень хоро́ший учи́тель».
While «до́брый» can mean 'good' in some set expressions, it's not the main meaning of the word in Russian. In most contexts, using «до́брый» to mean 'good' sounds dialectal or old-fashioned.
Хороший учитель means that he teaches well whereas добрый means that as a man he is good. But why "the" and not "a"? There is ni definite or undefinite article in Russian.
What's wrong with "a very nice teacher"? "Nice" and "kind" are quite synonymous.
Apparently not -- compare https://en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/%C4%8Ditati and https://en.wiktionary.org/wiki/Reconstruction:Proto-Slavic/u%C4%8Diti for the reconstructed Proto-Slavic roots.
The č in učiť, učiteľ apparently goes back to a -k (compare nauka "science") that presumably got palatalised before the -i- of the ending, and the u is part of the stem rather than a prefix to a stem čit-.
Does the audio sound right to you? To me, it sounds like "учитей" more than "учитель".
The quality of the audio is not too good. It’s very faint so it’s hard to make out what exactly is said there.
Because "dear" is дорогой.