(2) You keep stressing suite numbers and the proportion of rooms that are suites, but as I've been saying, it's much more complicated than this. You're looking only at the (short run fixed) supply.

There's also the demand side: Some hotels (luxury properties in particular and luxury resorts, plus hotels in certain major buiness cities and hotels where the clientele is likely to be generally wealthy) will have more (in absolute numbers) and more importantly a higher proportion of (paid) suite reservations. If you want a suite in Paris and are willing to pay for it, you're more likely to pick the PdG than the Marriott Rive Gauche and moreover more (in terms of absolute numbers and fractions) people will want suites in Paris than in Marseille on average over the year. People reserving suites are more likely to go to Male for a vacation than Cancun or Alicante.

Demand and supply interact too: If one is building a new (luxury, let's say) hotel or renovating one, you're award of how many suites you predict can be sold at what prices (depending of course on the hotel's location, features, etc. as well as the description of the suite), so if people will be more willing to pay for suites at your hotel, your akek sure that your hotel has more suites, in terms of numbers and the proportion.

Perhaps the best chance to get a suite would be when the (actual or expected) demand for suites is low relative to the asupply of suites. Off season travel is one example, but others would be weekday versus weekend arrival, (lack of) special events (don't expect a suite upgrade during the Olympics), etc. A good circumstance would be the hotel that has had a last minute wedding cancellation (for example, so that actual demand for suites has suddenly dropped) or a hotel located in an area experiencing an unexpected disturbance or disaster (Tokyo in the months after the Fukushima earthquake nuclear power plant disaster or Hong Kong currently).