Starting up is a big decision, you don't want to commit to...

Starting up is a big decision, you don't want to commit to starting your mine and find in 12 months that the spot price stagnated or went backwards and now that you're flooding it with an extra mine's worth of product it dips further (spot market is quite illiquid); overreliance on spot price absolutely crushed some big names after the last boom even after they had a year of selling into sky high prices. Generally contracts have a fixed price component and a spot % component, this can provide safety for both parties, & AFAIK current sentiment is that contracts of maybe >5yr length also expose parties to a lot of risk and are not desirable (impression I got from various CEO interviews), relative to the pain the "losing" party feels if the market changes a lot.

Regarding your other question about "strong pricing", $45/lb uranium is not "strong pricing", it's just 50% more than the rock bottom pricing we had a few months ago. Extremely few uranium mines are profitable selling at $45/lb. This fact, combined with the existing yearly deficit, is why people are currently valuing lots of companies in the sector at $1B+ despite them having negative NPV at current spot price.

& also w/r/t your comment on spot vs contract pricing flipping recently - not exactly the case. Contracts are generally formed at higher than spot price*, some leftover contracts today from a long time ago are still up in the $50/lb+ region, new contracts today would be quite unlikely to be signed at less than current spot price. If you look at https://www.cameco.com/invest/markets/uranium-price-sensitivity - yes, at $45/lb spot, Cameco are probably only getting $42.50/lb so a slight discount, but remember these are layered contracts from the last few years intended to protect them with $30/lb prices when spot falls to $20/lb, with corresponding concessions made to give the utilities a discount if spot goes high. I wouldn't be surprised if some of those old contracts sell at <$40/lb with spot @ $45/lb, while newer ones deliver parity or better at that spot price (pure speculation though). There's also speculation that Kazatomprom's recent large scale contracting with Chinese utilities occurred well above spot; again, mostly just hot air, but it gives you an idea of the semi-educated guesses of those familiar with the sector.
* I believe the exception was the blow-off top in spot in the previous run. Other than that it's pretty consistent.

A great article to read is "Would you have made a fortune in the uranium bull market?", google it, the original blog is down but it's rehosted as a pdf in a few places. It's very balanced despite the word "fortune" being in the title; the question is quite thoroughly investigated and by the end it's honestly hard not to answer "No", & I'm not expecting to stay in this one long enough to make a fortune either, even if the multiples work out that I might have been able to if I held it all to near the top

IMHO 2022 may be the big year for uranium but I also wouldn't be surprised if either (1) we stagnate and the thesis doesn't eventuate fully for another year or more, or (2) if the thesis does eventuate from here, we "only" get another 2-3x of "safe" growth before a blow-off top and subsequent pain. By "thesis eventuates" I mean contracting occurs at scale and at increasing prices in the $50, $60, $70+ range.