Why is は (ha) pronounced as わ (wa)? I mean I don't hear people say "owaiyogosaimasu", for instance. Someone please explain.
For the most part, pronunciation is very straightforward with Japanese. But there are a few exceptions. The pronunciation of the particles は, へ, and を are wa, eh, and o, instead of ha, he, and wo. Also, you'll find some words have "silent" vowels, like です (usually pronounced "des", rather than "desu") and 好き (usually pronounced "ski", rather than "suki").
は is like talking about the subject. If someone were to say " Sumimasen, Tanaka-san wa Nihon jin desu ka?" (Excuse me, Mr. Tanaka, are you Japanese?) Mr. Tanaka would probably say his response and then say, "Honda-san wa?" as if saying "And you?" in English. It basically is talking about the subject of the sentence.
well, the は pronounced like "wa" is just in the case that it's used like verb to be, like "omae wa mou shindeiru", but in all other cases is "ha", like "haha" that is "mom".
here is some reference to that: https://www.japanesewithanime.com/2017/08/particles-pronunciation-ha-wa-he-e-wo-o.html