In what way does technical analysis involve astrology and reading tea leaves?

I think that your source of information is conflating different things.

Tea reading is one of dozens of methods of fortune telling. If you believe that the market can be predicted from any of these, man, have I got a bridge to sell to you. Regards from Miss Cleo, RIP.

Astrology attempts to divine information about human affairs and other events by observing the movement of planets and stars which is constant. The study of planets and stars is a true science. AFAIC, applying astrology to the chaotic movement of the stock market is a pseudoscience.

There is some merit to some aspects of technical analysis. It can identify current momentum, the trend, areas of support and resistance but the bulk of it is a reflection of past price and/or volume movement and it predicts absolutely nothing going forward. It's like looking in the rear view mirror and expecting that to tell you where you are going. Any trade that you take based on such analysis is based on the HOPE that whatever trend or momentum you have identified will continue.

People talk a good game about different indicators but when you utilize them in real time (not curve fitted historical performance) none perform spectacularly. The next time you come across someone who tells you how great technical analysis is, ask them to post their picks in real time so that the picks can be monitored for performance. Chances are, you’ll get a bunch of excuses and no picks.

If TA indicators really did work, why would anyone invest/trade based on any other criteria? Why would anyone ever lose money? Why would anyone ever take the other side of the trade if the future was predictable?

It's an analogy.

In general, many hold the belief that the typical traders (read: not Warren Buffett levels of money where the simple act of trading can change the market) cannot beat the market in the long run. "Wisdom of the crowd" and all that — everyone has already made their best guess what the price should be and the average of those guesses is probably much better than your guess alone.

So technical analysis can very much be seen as "reading tea leaves". You look at a whole bunch of indicators and see what you want to see. Another person looks at the same indicators and sees something completely different. If you're successful, it feeds confirmation bias. When it fails it's written off as a fluke.

In many ways it reminds me of sports prediction before statistical modeling took over. You had all the so-called experts who lived and breathed the sport their whole lives making predictions and they were pretty terrible at it. Then people treated it like a data analysis problem and did extremely well. The main reason? There were all these stats (much like in technical analysis) but people just aren't very good at understanding how all those variables interact. People are quite good at seeing single variable relationships, but they are terrible at multivariate problems. Once you get more than a couple of variables, people can no longer keep track of how all of them interact and feed into the outcome.