pre_get_posts with meta_query effects static pages in WooCommerce - php

Question

I used a big part of this code to add a meta_query in the WooCommerce product query. I don't get any errors, but the products are NOT getting filtered by the meta. It still shows all products.
function yl_custom_product_query( $query ) {
// check if the user is requesting an admin page
// or current query is not the main query
if ( is_admin() || ! $query->is_main_query() ) {
return;
}
global $product;
$blog_id = get_current_blog_id();
if ($blog_id == '1') {
$subsite = '_visibility_3rdmillennium';
} elseif ($blog_id == '2') {
$subsite = '_visibility_fight2win';
} elseif ($blog_id == '3') {
$subsite = '_visibility_muaythai';
} elseif ($blog_id == '4') {
$subsite = '_visibility_taekwondo';
} elseif ($blog_id == '5') {
$subsite = '_visibility_xprtfightgear';
} elseif ($blog_id == '6') {
$subsite = '_visibility_hayabusashop';
} elseif ($blog_id == '7') {
$subsite = '_visibility_kmushop';
}
$meta_query = array();
// add meta_query elements
if ( !empty( get_query_var( $subsite ) ) ) {
$meta_query[] = array( 'key' => $subsite, 'value' => get_query_var( 'yes' ), 'compare' => 'LIKE' );
}
// unused meta_query for now
if ( !empty( get_query_var( 'key2' ) ) ) {
$meta_query[] = array( 'key' => 'key2', 'value' => get_query_var( 'key2' ), 'compare' => 'LIKE' );
}
if ( count( $meta_query ) > 1 ) {
$meta_query['relation'] = 'AND';
}
if ( count( $meta_query ) > 0 ) {
$query->set( 'meta_query', $meta_query );
}
}
add_action( 'pre_get_posts', 'yl_custom_product_query' );
But, when I change:
// add meta_query elements
if ( !empty( get_query_var( $subsite ) ) ) {
$meta_query[] = array( 'key' => $subsite, 'value' => get_query_var( 'yes' ), 'compare' => 'LIKE' );
}
to
// add meta_query elements
if ( !empty( $subsite ) ) {
$meta_query[] = array( 'key' => $subsite, 'value' => 'yes', 'compare' => 'LIKE' );
}
(so removing get_query_var twice) the meta_query works great but all static pages suddenly become unreachable...
What am I missing here?