This may be because such extrinsic incentives may replace (partially or in whole) intrinsic and reputational incentives, motivating the person to focus on obtaining the extrinsic rewards, which may make the thus-incentivized behaviors less desirable.
ðɪs mˈeɪ biː bɪkˈʌz sˈʌtʃ ɛkstɹˈɪnsɪk ɪnsˈɛntɪvz mˈeɪ ɹᵻplˈeɪs pˈɑːɹʃəli ɔːɹ ɪn hˈoʊl ɪntɹˈɪnsɪk ænd ɹˌɛpjuːtˈeɪʃənəl ɪnsˈɛntɪvz, mˈoʊɾᵻvˌeɪɾɪŋ ðə pˈɜːsən tə fˈoʊkəs ˌɔn əbtˈeɪnɪŋ ðɪ ɛkstɹˈɪnsɪk ɹᵻwˈɔːɹdz, wˌɪtʃ mˈeɪ mˌeɪk ðə ðˈʌsɪnsˈɛntɪvˌaɪzd bᵻhˈeɪvjɚz lˈɛs dɪzˈaɪɚɹəbəl.