Blu-ray is lossy too. All video codecs of note that aren't for professionals are lossy, so the point mostly still stands. Lossless compression doesn't go very far when it comes to video.

An uncompressed 24 bit 1080p image is just under 6 MB. If you save it as a compressed PNG, you cut that down to roughly 2.5 MB. Now, PNG compression isn't very efficient, and you can probably do some interframe magic if you really wanted to (cf lossless h264), but the whole exercise is mostly futile, since even if you cut your bitrate down to an eighth, you're still looking at, like, 20-ish minutes of runtime with 25 gigabytes.

Meanwhile, blu-ray looks as good as it does at an average of 25-30 mbit/s (0.03 gbit/s) (while UHD blu-ray even more so, with a better codec, so even more detail is preserved). The compression used saves so much space the trade-off is obviously worth it unless you're a production company making an actual movie, where every detail counts.

Ah, that's what it was. I'm still half asleep, I didn't drink enough caffeine this morning haha