Unless you have a space leak, how is laziness a weakness there?
I've had issues with lazy IO that caused awkward behaviour. Identifying the root cause was not trivial, and altogether, laziness gave me no benefit and caused me lots of harm. This is the most important point here: when laziness is useful very rarely but causes non-trivial trouble often, why on earth have it on by default?
I'm sorry that I cannot remember the specifics of my problems, this project was done years ago.
Haskell has lots of fundamental weaknesses when it comes to long-running real world programs, laziness being the most obvious one.