The answer is in the JavaDoc of the equals() method:

Unlike compareTo, this method considers two BigDecimal objects equal only if they are equal in value and scale (thus 2.0 is not equal to 2.00 when compared by this method).

In other words: equals() checks if the BigDecimal objects are exactly the same in every aspect. compareTo() "only" compares their numeric value.

As to why equals() behaves this way, this has been answered in this SO question.

The general rule for equals is that two equal values should be substitutable for one another. That is, if performing a computation using one value gives some result, substituting an equals value into the same computation should give a result that equals the first result. This applies to objects that are values, such as String, Integer, BigDecimal, etc.

Now consider BigDecimal values 2.0 and 2.00. We know they are numerically equal, and that compareTo on them returns 0. But equals returns false. Why?

Here's an example where they are not substitutable:

var a = new BigDecimal("2.0");
var b = new BigDecimal("2.00");
var three = new BigDecimal(3);

a.divide(three, RoundingMode.HALF_UP)
==> 0.7

b.divide(three, RoundingMode.HALF_UP)
==> 0.67

The results are clearly unequal, so the value of a is not substitutable for b. Therefore, a.equals(b) should be false.