They should have put it on a blu-ray disc. Blu-ray is perfectly capable for branching video. I have plenty movies with different director's cut and final cut etc on the disc, it doesn't store the whole thing 4 times like this 75gb for 4 x 22 minute episodes seems to suggest.
Dunno what codec they used for this but it seems very lazy. h.265 could store over 9 hours of blu-ray quality video in 75GB. 75GB for 9 hours comes to 19 mbps, a bit higher than 4K Netflix with HDR. Comparable to avg 28 mbps h.264 + 5 mbps for DTS HD MA.
Bandwidth is cheap I guess, for some. At least if you only do one play through with streaming it shouldn't take too much of a data cap.







