Why does Google trim the advertisers candidates?

Google trims the number of advertiser candidates primarily to manage the computational load involved in calculating quality scores in real-time. Initially, thousands of advertisers might be considered for a keyword, but Google narrows this down to a few hundred promising candidates. This allows for more efficient scoring and a streamlined auction process, ultimately resulting in the selection of one to four winners based on specific criteria^[1].

However, specific reasons for the trimming process were not detailed in the available sources, indicating a lack of detailed insights on this topic^[2].