It also takes time. You've doubtless seen headlines about the Contracts for Difference Allocation Rounds 7 and 7a, or perhaps even Round 8 taking place now.
But those headlines are about the step where you find out who won these auctions because that's when that magic price number is known, wind power for £68.35 per MWh or whatever.
Going from the fun headline to actual contract signing in which there's a legal promise to actually try to make electricity and get paid, takes several months. After they've signed they begin the actual work, which still includes planning not just the mechanical aspects.
Just building a solar farm might take 12 months, and wind farms are often slower.
AR6 took place in 2024, you'd have read headlines back then about some excellent solar farms, getting paid about £50 per MWh. First, those are 2012 prices, for comparison reasons they choose a base year and then calculate inflation adjusted pricing in reality but I bet that £50 figure was what you saw in a headline, of course the solar farm didn't exist in 2012, so £50 per MWh was never the real price.
More importantly though, those solar farms weren't built in 2024. The plan when the bids went in, said 2026/27 for some and 2027/28 for the majority. A few of those AR6 solar farms (by no means the majority) were live in time for the July sunshine, in 2026. But you've already read headlines about AR7, and like I said maybe even AR8.
A big boost in practice is home install. A big business can take six years to do contract paperwork, get something signed off, build it and then commission it. A home owner is angry after six weeks without work done. Where are my fucking panels? You were going to install solar panels, make it happen! So lots of individuals and small businesses which own a building with a roof installed a few panels, they might add up to only 5kW each but if a million people do that it's 5GW of nameplate electricity generation, a sizeable fraction of UK usage for several hours per day.