The fact that Lillee did not succeed there. This is fact.
"Lillee did not succeed" and "Lillee failed conclusively" are not the same thing. If Lillee had played 5 series in the subcontinent and failed in the whole lot, it's very probable only the most ridiculously partisan Australians would still be capable of claiming him the greatest seamer of all-time.
However, either of them would be damning when he is compared to other brilliant bowlers, bowlers who could do everything he could - and some even do things he couldn't (no-one, and I mean no-one, would claim Lillee was as accurate as McGrath and Ambrose; he didn't need to be, he could still be a brilliant bowler without being so, as McGrath and Ambrose didn't need to bowl big hooping outswingers like Lillee did, because they could bowl such good off-cutters and leg-cutters, and use the seam, and be brilliant bowlers with that and their phenominal accuracy). Now, only one of them can have happened, and only a fool would call him a proven failure because of a single series and a one-off Test years later. Had Lillee been a proven failure in the subcontinent, obviously, it wouldn't matter a damn to what he'd done elsewhere; and in any case, there's no reason to believe such a thing would have been likely.
But there is no two ways about the fact that Lillee did not succeed in the subcontinent, and I'll say it again, it annoys me when people tell me that, by saying that, I'm saying something I'm not.