According to Bulbapedia, the encounter rate is determined by the simple formula P = x/187.5, where x is the following:
Rarity of Pokemon x
Very Common 10
Very Rare 1.25
Based on the Pokemon that are in the area, you can use the formula to get the chance a Pokemon will appear. The higher the chance is of a Pokemon appearing, the greater x will be, and therefore, the higher chance you'll have to encounter a Pokemon. In Solacean Ruins, the only Pokemon there are Unown, meaning you have a 100% chance of encountering it. This means that x = 10, making the probability 5.33% of enountering Unown, and basically, 5.33% chance of encountering any Pokemon at all. In Wayward Cave, however, you have different encounter rates that will factor in, as there are more Pokemon to work with. With all these additional Pokemon, chance will increase, as you have the chance each Pokemon a certain percentage, and the summation of these percentages will equate to something decently high, which explains your Wayward and Solceon Ruins problem.
Also, this is partially luck based, evidently. You were probably just unlucky with your encounters in Wayward rather than Solaceon. There may have also been certain Pokemon that have abilities that alter encounter chances:
- Intimidate / Keen Eye: Reduces the encounter rate. If the Pokemon is more than or less than 5 levels than the lead Pokemon that has Intimidate / Keen Eye, the Pokemon's encounter rate is reduced by 50%.
- Arena Trap / Illuminate: If the lead Pokemon has the ability, the encounter rate doubles.
- Pressure / Vital Spirit / Hustle: If the lead Pokemon has this ability, than the chance that higher level Pokemon than it appear is inceased by 50%.
- No Guard: If the lead Pokemon has this ability, than the encounter rate is increased to 150%.
- Quick Feet / Stench / White Smoke: If the lead Pokemon has these abilities, the encounter rate is halved.
- Sand Veil: If the lead Pokemon has Sand Veil, the encounter rate of Pokemon found in areas of sandstorm is halved.
- Snow Cloak: If the lead Pokemon has Snow Cloak, the encounter rate of Pokemon found in areas of blizzards is halved.
- Suction Cups / Sticky Hold: If the lead Pokemon has this ability, the rate Pokemon encountered during Fishing increases.
- Swarm: If the lead Pokemon has this ability, the rate wild Pokemon appear doubles.