Judging from the manual, the 74924 comes with the ramps already attached to the track where the 74923 requires the customer to attach the ramps to the track.

The maximum voltage went down from 22 V (74923) to 19 V (74924).
Since both sets can be expanded with the 74930 set, there must be a way to remove at least one ramp from the track.

Maybe Märklin can explain what changed "under the hood".

I didn't contact them.
If you receive a response, please share it with us.
In my experience they answer less than 50% of technical inquiries and 50% of the replies are completely useless, but such a simple question may yield some useful insights.

Thanks Tom for your honesty. Whenever I have asked a question directly to Marklin, I either don't get a reply or the reply comes months later, and by then I've either abandoned the process or I've managed to find the answer from elsewhere. They don't seem to like to be helpful to their customers - Very strange.