Understanding Society User Support

I am facing issue while merging the data. I have created one dataset using well-being indicators from indresp files for all waves. This dataset also has hidp, msoa and lad. Second dataset is for cultural indicators for only two waves "b" and "e" and I have kept them separately as two years.

Now, when I am merging wellbeing all wave with culture wave b using person_id which is pidp only 67 obs are matching. Please help me what is causing the issue in merge. Do I have to use some other variable to merge?

merge m:1 person_id using "C:\WISERD\Culture\Culture_Ind_KEY_1011.dta"
(variable person_id was float, now double to accommodate using data's values)

Result                      Number of obs
    -----------------------------------------
    Not matched                       577,701
        from master                   527,539  (_merge==1)
        from using                     50,162  (_merge==2)

Matched                                67  (_merge==3)
    -----------------------------------------
for cultural wave e:

. merge m:1 person_id using "C:\WISERD\Culture\Culture_Ind_KEY_1314.dta"
(variable person_id was float, now double to accommodate using data's values)
(variable household_id was float, now double to accommodate using data's values)

Result                      Number of obs
    -----------------------------------------
    Not matched                       566,802
        from master                   527,115  (_merge==1)
        from using                     39,687  (_merge==2)

Matched                               491  (_merge==3)
    -----------------------------------------