Pure tautology then
'Microsoft Defender, being part of Microsoft 365, can't be purchased as a stand-alone product. The CMA did say that user numbers taking advantage of Microsoft's solution are "both very high and growing very fast" but were not included in the analysis due to its inclusion in Windows.'
As the AV is included, the growing numbers reflect only the increase in Windoze subscriptions. Consequently this statement is pointless (all the more as the figures were not used).
Typical HMG departmental bloatspeak (or alternatively as W S Gilbert famously stated "merely corroborative detail to add artistic verisimilitude to an otherwise bald and unconvincing narrative" The Mikardo (1885)