Why doctors allow several MMA fights in the same night but not in a few days?

https://www.iscfmma.com/ISCFRules15.htm (mirror) gives the explanation:

Time Between Bouts
This new rule is to avoid a fighter, fighting on a "Different Promotional" event less then 7 days after a fight or a fighter fighting too soon after being defeated by a Knock Out or TKO by too many striking blows.

• If the fighter is fighting in a TOURNAMENT within a 3 day time span and does not lose by KO/TKO and is not cut or injured during their bout, the "Time Between Bout" Rule does not apply.

  • 6-08: Fighters in a TOURNAMENT MUST be checked by a Licensed MD after EACH BOUT to assure they are in good health to continue to the next round.

• TIME BETWEEN BOUTS

  • 7 days or 168 Hours before stepping into the ring or cage to fight again.
    • Example: If you fight on Friday night the 1st at 6:PM, you cannot fight again until the following weekend, Friday night the 8th at 6:01 PM
      • There are other reasons for this rule as well. These reasons will also explain why a fighter can fight multiple times within 2-3 days if only on the SAME event. Such as;
        • It stops a fighter from booking back to back fights where as the second fight's promoter risks him not being on his event if injured the week before.
        • It gives the sanctioning bodies and the MMA Databases a chance to make sure all the fighters results are made public. An amateur fighter could fight as a pro and turn around and fight as an amateur a week later because the news had not gotten out yet he fought pro.
    • FINE & SUSPENSION: If ANY AMATEUR fighter is caught breaking this rule, by fighting for another organization or on an unsanctioned event within 7 days of an ISCF Sanctioned event, that fighter will be suspended from competing by the ISCF for a minimum of 60 days and fined a Medical Rest Period Fine of $250.00. Suspension will remain until fine is paid.