What happened to Microsoft and Alphabet does not seem comparable to Sears, GE, Boeing, and IBM. The latter group have objectively declined in terms of profit and potential.

MS/GOOG are still earning near record amounts of net income with fat profit margins, and have a higher than ever market cap.

AMZN also, so far, has pretty rosy numbers to back it up. They’re profit margins are relatively tiny though, so the executives are focusing on increasing those to match its trillion dollar market cap.

It is the reason Amazon shareholders enjoy a $2T market cap rather than Walmart shareholders that only have a $650B market cap.