There are still (a few) people practicing alchemy somewhere, though it clearly doesn't have the kind of weight that something like astrology does.

For starters, alchemy is not an ideal pseudoscience in terms of long-lived-ness because it generally had some very specific aims, notably transmutation of base metals and elixirs of life and that sort of thing, which it has consistently and clearly failed to produce. Astrology, on the other hand, tends to make vague predictions which are much harder to pin down.

The other thing is that alchemy doesn't have a great deal of personal appeal, whereas astrology is much more individual-oriented. It's your future being predicted, it's something relevant to you. That's much more exciting for the average person than some recipe for a particular substance. Hermeticism is a somewhat more spiritual branch of the discipline and it is largely that which survives in the present day.

To somewhat oversimplify, the spiritual and protoscientific aspects of alchemy were pretty heavily intertwined until the Renaissance, at which point they seem to separate. There is currently some debate within the literature about how important the 'spiritual' aspect of the discipline was - some historians allege that this aspect was played up by Victorians, who may have adulterated earlier texts.

In their search for lofty goals like transmutation of base metals into gold, alchemists made numerous discoveries (frequently accidentally) that were actually useful - they made great contribution to metallurgy, tanning, dyework, paint &c, invented distillation, began classifying and grouping materials based on their properties and the like. These haphazard exploratory pieces of research would lay the foundation for a more rigorous chemical science.

Robert Boyle is the traditional 'Father of Chemistry', though how separate he was from alchemy as a movement is, again, a topic of debate. His significant step forward was his detailed and rigorous recording of all possibly relevant conditions. As Boyle and other early 'chemists' began working with more rigour and effort to systematise, the non-spiritual aspects of alchemy just became chemistry.

To distill down this answer to its most fundamental: alchemy and astrology were both looked down upon at some points in history. Alchemy stayed down easier because it required a lab and was extremely expensively to do seriously. All you need for astrology is a book and a chart of the planets and stars at a given time. Or say, just a calendar.

Astronomy was improved in order to have better (more accurate) horoscopes. So astrology actually help astronomy move forward. Alchemy also moved science along.. but was eventually just replaced by it altogether.

But the best astrologers became the best astronomers. Kepler was known for his horoscopes. Tycho Brahe had the most precise measurements pre-telescope (with equipment that was up to three stories tall!).. and also gave royal horoscopes.

The history of science isn't as straightforward as it often seems. The printing press spread magic spells and occult beliefs faster and sooner before it started spreading scientific knowledge... the printing press actually brought on a renaissance of magic, just as it brought on the reformation by spreading those ideas.