我用cmp命令做工具变量回归和手动做两阶段回归，前者显著，后者不显著，是啥原因？难道是我的手动两阶段命令有误吗？

cmp命令如下：
cmp (occupdegree = communityD21b ageA1 age2  genderA2 mzA3 eduA6 marriageA14 healthA23 partyA7 leaderA9 certificationA11 citytimeA17 firworktimeA27 empexchangeB1 emptimeB2 familysq workingtime city industryB15a fatherjobG1C1a) (communityD21b = AQ), ind($cmp_oprobit $cmp_probit) tech(dfp) nolr

communityD21b 是内生变量，AQ是工具变量


手动两阶段工具变量回归命令如下：
probit communityD21b ageA1 age2  genderA2 mzA3 eduA6 marriageA14 healthA23 partyA7 leaderA9 certificationA11 citytimeA17 firworktimeA27 empexchangeB1 emptimeB2 familysq workingtime city industryB15a fatherjobG1C1a AQ, vce(robust)

predict a

oprobit occupdegree a  ageA1 age2  genderA2 mzA3 eduA6 marriageA14 healthA23 partyA7 leaderA9 certificationA11 citytimeA17 firworktimeA27 empexchangeB1 emptimeB2 familysq workingtime city industryB15a fatherjobG1C1a, vce(robust)