Main reason for rejection of Schengen visa lies in stay documents: Anitta Hipper of European Commission (home affairs)

livemint.com:

Worldwide, travellers are unhappy with the delay in Schengen visa processing times that is impacting their personal and professional travel plans. What’s the big reason for this delay?  In India, people are complaining that scheduling an appointment ‘takes forever’. How can this be expedited?  This is not a specific situation to India.

The European Commission has received numerous reports from visa applicants who, in various geographical locations, have difficulties obtaining an appointment for the submission of a visa application at Member States' consular offices. Travel restrictions related to COVID-19 have forced some Member States to reduce the number of staff engaged in consular offices or have had to cancel their contractual arrangements with external service providers. In a context of resumption of international travel and increase in visa applications, the pressure in some places creates difficulties for service providers and consulates in processing an increasing number of visa applications in a timely manner.

In addition, intermediaries use sophisticated IT tools to book appointments on behalf of visa applicants as soon as they are released, making extremely difficult for applicants not using their services to book an appointment on their own. The Commission regularly calls on the Member States' visa authorities to improve their operational capacities and address this issue by releasing more appointments. As for the decisions on visa application, the decisions in this matter are the exclusive competence of Member States.