Why does GNU ELPA have old package versions?

[Jorge P. de Morais Neto]

Hi.  I noticed for several packages that GNU ELPA has older package
versions than MELPA and often even older than MELPA-Stable.  Below are
packages (with names from A to F) that appear both in GNU and
MELPA-Stable, but with different versions:

| Package           |     GNU | MELPA-Stable |         MELPA |
|-------------------+---------+--------------+---------------|
| aggressive-indent |   1.8.3 |        1.9.0 | 20200512.1207 |
| beacon            |   1.3.3 |        1.3.4 | 20190104.1931 |
| coffee-mode       | 0.4.1.1 |        0.6.3 | 20200315.1133 |
| company-math      |     1.3 |          1.4 | 20200131.2337 |
| counsel           |  0.13.1 |       0.13.0 | 20200619.1030 |
| fountain-mode     |   2.7.3 |        3.1.0 |  20200620.659 |

So except for package `counsel' (out of six analyzed packages), the GNU
ELPA version is even older than MELPA-Stable.  Why is that?  Does GNU
ELPA have additional quality checks before including a new package
version, or is it just undermaintained?  I prefer to use official GNU
software, as it generally has superior quality and ethics.  However, I
also love running the latest semi-stable version of important packages;
for example, I write this on GNU Emacs 27.0.91.

Regards

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