If you do normals you only get 489/496 ilvl instead of 502 ilvl WITHOUT completing the legendary quest chain.
If you actually put an heroic group together you got 502/509 ilvl WITHOUT completing the legendary quest chain.
Instead of asking my friends "Hey, you wanna do that content we farmed for months on our alts!" only to get worse gear / the same gear without completing the legendary quest chain.
No, I rather put less effort and less time in by just afking through LFR to get better loot + completing the legendary chain without bothering my friends by trying to drag my friends with on old content.
If T14 gave better loot than LFR and LFR did not complete the legendary chain your points would be viable, but right now they arent.
If that is so hard to understand I dont know what.