Because of the nature of the game, a player’s odds in blackjack are constantly changing. Well, they used to at least.
Because of the constant shuffling method of operation of a Random Number Generator (RNG) in online blackjack and the Continuous Shuffle Machines (CSM), the odds in those blackjack games stay pretty fixed. The reason for why the odds on those two types of blackjack stay the same, roughly, is because in regular blackjack the remaining deck changes.
A player’s blackjack odds traditionally shift throughout the course of the game. When a round ends, the cards that were just played are collected and set aside as discards. In other words, they are no longer in play.
With cards being removed from play it affects what the percentage of cards that are left in the deck. For example if there has been a run of low cards, it means that more low cards were being dealt and then removed from play at the end of each round. With those low cards gone, it leaves a greater number of high cards left to be dealt. A shift in cards like that is what causes the odds in blackjack to change.
When there has a been a run of low cards, like in the scenario above, the remaining high cards in the player’s favor, increasing the player’s blackjack odds. With high cards remaining there is an increased chance of being dealt a natural blackjack or having high double downs, both of which pay more and take away more from the house’s edge.
But when the run was a high card fun and the remaining deck is rich in low cards, it means a decrease in the player’s blackjack odds. This is because low cards favor the house and not the player. Dealers are more likely to hit to strong hands while a player busts or loses because of a stiff hand.
Because an RNG pulls from dealing outcomes that include all the cards in a deck it means that no cards are left out of the outcomes. This is similar to a CSM in that all cards are in play at all times.
This is can be good and bad. It is good because it means that the house does not have an advantage at times; but it is also bad because the player does not have an opportunity to have increased blackjack odds from discarded cards.