Csgo: No rank up after 8 wins in a row (Including a tie)

As we don't have access to the ELO points system that is used to calculate player ranking there is no way of knowing exactly why you didn't rank up.

But take a look at the below post, which does a good job of explaining the basics of how ranking works:

CSGO Ranking Explained - The In-Depth Guide

It includes some details from Wikipedia about how the ELO Rating System works in general:

The Elo rating system is a method for calculating the relative skill levels of players in competitor-versus-competitor games such as chess.

The difference in the ratings between two players serves as a predictor of the outcome of a match. Two players with equal ratings who play against each other are expected to score an equal number of wins. A player whose rating is 100 points greater than their opponent's is expected to score 64%; if the difference is 200 points, then the expected score for the stronger player is 76%.

A player's Elo rating is represented by a number which increases or decreases based upon the outcome of games between rated players. After every game, the winning player takes points from the losing one. The difference between the ratings of the winner and loser determines the total number of points gained or lost after a game. In a series of games between a high-rated player and a low-rated player, the high-rated player is expected to score more wins. If the high-rated player wins, then only a few rating points will be taken from the low-rated player. However, if the lower rated player scores an upset win, many rating points will be transferred. The lower rated player will also gain a few points from the higher rated player in the event of a draw. This means that this rating system is self-correcting. A player whose rating is too low should, in the long run, do better than the rating system predicts, and thus gain rating points until the rating reflects their true playing strength.

It also includes some information about how this is applied in CSGO, when it's 5v5:

...every round (please bear in mind every ROUND, not every game) will be treated like a single game of chess wherein the team with higher Elo Points is expected to win. Each team consists of 5 players which may or may not have the same rank, therefore their total Elo Points will be considered for the purpose of prediction. Consequently, a player with less Elo Points than the rest of the team would lose (give to the enemy team) less points than one with more points in case of a Round Loss and vice versa.

So say you were on the better team, and you were one of the better players (points wise), if the matches were close (or you drew), you could still actually lose more points than you gain as you were expected to win more of the rounds. Each rank is made up of a range of points, so clearly with your matches you didn't accrue enough points to cross the range to rank up.

Having a greater margin of round wins, say 16-5 vs 16-14 would give you more points, and the other factor appears to be MVPs, so if you have the bomb, try not to drop it for a team mate as you would get more points for a plant. Similarly, if you're on CT, buy a defuse kit as defusing gives you more chance of an MVP and gives you more points.

From my experience, it's completely random.

I ranked up from GNM to MG1 then next game I played after I ranked up the enemy team surrendered and I ranked up to MG2.