grammatically speaking...

[Arnold Zwicky]

re "explain me what you mean":

there's a much larger, and fairly well studied, phenomenon of
which this is just one example: the alternation between prepositional
and unmarked indirect objects, as in GIVE THE MONEY TO ME ~ GIVE ME
THE MONEY.  verbs of transfer (literal or figurative) generally allow
the prepositional construction, but only a few allow the unmarked
construction (DONATE THE MONEY TO US, but *DONATE US THE MONEY).
the big generalization seems to be that if you understand the semantics
of a verb of transfer, you'll get it in the prepositional construction,
but to get it in the unmarked construction you probably have to hear
someone use it there.

the full set of facts is a bit more complicated than this, since there's
a least one class of transfer verbs (denominal means-of-communication
verbs like TELEPHONE, FAX, and XEROX) that seem to allow the unmarked
construction directly.  it's also true, as many writers have noted
(going back to georgia green's ph.d. dissertation, at least), that
speakers sometimes extend the unmarked construction to new verbs within
semantic subclasses.

but mostly it seems to be "what you hear is what you get".

EXPLAIN is a figurative transfer verb.  for most speakers, it doesn't
allow the unmarked indirect-object construction.  it's like DONATE.

not everything has a deeper explanation.

arnold (zwicky at csli.stanford.edu), who does indeed know about
  proposals that the number of syllables, stress pattern, and/or
  anglo-saxon stratum of the vocabulary are determinants, but thinks
  these ideas won't fly when you look at the facts in detail