I wonder where you are getting that from?
pressgazette.co.uk/most-popular-newspapers-uk-abc-monthly-circulation-figures/
According to this several newspapers including the Guardian don't disclose their circulation numbers anymore. From the article:
The above figures do not include the Sun, Times and Telegraph titles which have all chosen to keep their ABC circulations private since the start of 2020. The Guardian and Observer joined them in September 2021.
The last ABC figures we have for these titles are as follows:
The Sun: 1,210,915 (March 2020)
The Sun on Sunday: 1,013,777 (March 2020)
The Sunday Times: 647,622 (March 2020)
The Times: 365,880 (March 2020)
Daily Telegraph: 317,817 (December 2019)
Sunday Telegraph: 248,288 (December 2019)
The Observer: 136,656 (July 2021)
The Guardian: 105,134 (July 2021)
Unless you mean subscriptions including the US where they have indeed grown their share. But in the UK, I believe they don't rank that highly in terms of circulation.