It's inaccurate to say they've never been competitive.
In 1977, they lost 3-1although the ABs were reduced to three-man scrums in the test at Auckland. Had it over us in the forwards, but we somehow snuck through.
In 1959, the Lions had great players like Tony O'Reilly and Dicky Jeeps. In the first test at Carisbrook, the Lions scored five tries to none - and lost. Don Clarke banged over six penalties (tries were worth 3 points in those days), and a lack of conversions cost the Lions the victory. ALthough that series was also won 3-1, only the third test (22-8) could be considered a blowout in favour of the All Blacks.
The 1983 side was competitive in all but the last test. They suffered from having the third-choice hooker, Ciaran Fitzgerald, forced upon them as captain.
The 1950 series was 3-0, but it was all square after the first test was drawn.
This series, however, has been rather lopsided.