How to transfer such parameters to the CNC?

Question

URL Handling

Hello everyone) help me figure it out plz:
RewriteRule ^catalog/$ /cat.php [NC]
RewriteRule ^catalog/(.*)/$ /cat.php?showcat=$1 [NC]
RewriteRule ^catalog/(.*)/( .*)/(.*)/$ /cat.php?showcat=$1&page=$2&ar=$3 [NC,L]
why is the showcat parameter passed on the second line, but not on the third? (I need to pass a different number of parameters, not always 3 of them at once)