A recent morphological change in American English is the mistaken substitution of the adjective/adverb begrudging(ly) for the normative grudging(ly). This has come about as an indirect result of the fading into obsoleteness of the verb grudge (intr. ‘to murmur; to utter complaints murmuringly; to grumble, complain; to be discontented or dissatisfied’), whereas its prefixed successor begrudge (‘to grumble at, show dissatisfaction with; esp. to envy [one] the possession of; to give reluctantly, to be reluctant’) is currently alive and well.
Beyond the particular morphology of the neologism, however, lies the general contemporary tendency in English toward hypertrophy, which in this case means the expansion of grudging(ly) by the prefix be-. This tendency includes the substitution of previously emphatic forms for their neutral counterparts, a process which always comports a difference in semantic grading. In the case of begrudging(ly), part of the explanation for the neologism would accordingly make reference to the felt need (by younger generations of speakers, but not only) to emphasize (heighten) the negative––i. e., uncharitable––meaning of grudging(ly), an end subserved by the prefixed form(s).