Why does android keep dx when it was replaced by d8?

Why does android still keep dx along its newer replacement d8?

$ cd cmdline-tools/build-tools/30.0.3 && ls d*
d8  dexdump  dx

Here is the program I used:

$ cat Primes.java
class Primes {
    private static boolean isPrime(int p)
    {
        for (int i=2;i<p;i++) {
            for (int j=2;j<p;j++) {
                if (i*j == p) {
                    return false; }}}
        return true;
    }
    public static void main(String[] args) {
        for (int i=2;i<100;i++) {
            if (isPrime(i)) {
                System.out.format("%d ",i);}}}}

And here is how I compile it to dex:

$ javac Primes.java
$ cmdline-tools/build-tools/30.0.3/dx --dex --output dx/classes.dex Primes.class
$ cmdline-tools/build-tools/30.0.3/d8       --output d8             Primes.class
$ cmdline-tools/build-tools/30.0.3/dexdump -d dx/classes.dex > dx.human
$ cmdline-tools/build-tools/30.0.3/dexdump -d d8/classes.dex > d8.human

Then I clean up addresses, register names and comments to be able to compare:

$ cat dx.human | awk "/\'main\'/,/catches/" | sed "s/.*|[0-9a-f]*: //g" | sed "s/\/\/.*//g" | sed "s/Ljava.*//g" | sed "s/v[0-9]/v/g" | sed "s/v[0-9]/v/g" > dx.main.human
$ cat d8.human | awk "/\'main\'/,/catches/" | sed "s/.*|[0-9a-f]*: //g" | sed "s/\/\/.*//g" | sed "s/Ljava.*//g" | sed "s/v[0-9]/v/g" | sed "s/v[0-9]/v/g" > d8.main.human

They are almost identical then, but not entirely:

$ diff -u dx.main.human d8.main.human
--- dx.main.human   2021-04-12 19:49:37.110476376 +0300
+++ d8.main.human   2021-04-12 19:49:44.650101698 +0300
@@ -2,11 +2,11 @@
...
-      registers     : 7
+      registers     : 5
...
 const/4 v, #int 2 
 const/16 v, #int 100 
 if-ge v, v, 001f 
@@ -14,13 +14,13 @@
 move-result v
 if-eqz v, 001c 
 sget-object v, 
-const-string v, "%d "  <----------------+
 const/4 v, #int 1                       |
 new-array v, v, [                       |
 const/4 v, #int 0                       |
 invoke-static {v},                      |
 move-result-object v                    |
 aput-object v, v, v                     |
+const-string v, "%d "  <----------------+ 
 invoke-virtual {v, v, v}, 
 add-int/lit8 v, v, #int 1 
 goto 0001 

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