I am just guessing (and you should contact Seven Bridges for an authoritative reply) but maybe it is due to licensing issues: GATK up to 3.8 is not free for commercial use - GATK 4.0 onwards will be free for any use. So maybe they acquired a license for this particular version but decided it wasn't worth to pay for the upgrades, for whatever reason.
Again, just guesses, yours will be as good as mine. Contact Seven Bridges for a proper answer.
Thany you for your answer I send an e-mail to Seven Bridges' support team, but two days passed and no reply....