The default is the whole point. Almost any language can support lazy evaluation, given enough boilerplate, but laziness-by-default is a major contributor toward making Haskell code more composable and reusable compared to idiomatic code in other languages.

In strict-by-default languages one must decide up front whether to permit evaluation to be deferred, and there is a cost to be paid via more awkward syntax to first capture the deferred computation and then explicitly evaluate it. This also tends to add runtime overhead which a Haskell compiler would optimize out in cases strict evaluation can be inferred. As a result, libraries generally expose only strict interfaces—and while most lazy functions can easily be made strict in Haskell with judicious application of `seq`, the reverse is not so simple.

Sure, sometimes excessive laziness becomes a problem. However, these cases are not that common, or particularly difficult for an moderately experienced Haskell coder to identify or work around. Enforcing strictness-by-default just because one does not foresee a need for laziness, without any evidence that laziness is negatively impacting performance, would be a form of premature optimization.