Because of some Twitter limitations, occasionally you may not see the full list of likers or retweeters to block.
Each Block List has a maximum of 5000 users
Each block list can block up to 5000 per list, based on standard Twitter API rate limits. You may create as many lists as you need to block more users.
Some of the liking/retweeting users have protected their Tweets.
Accounts that have chosen to protect their Tweets still count towards the like and retweet statistics you can see on Twitter, but it is not possible to identify which of these accounts have liked or retweeted a Tweet.
More users have liked/retweeted since you created the block list.
In the time it takes to block all the users in a Block List, more users could have liked/retweeted the Tweet. You can make another block list to find more users.
You have blocked every user already.
You may have blocked some of the users in previous Block Lists, from your Lockout Folder, or on Twitter.