Why SQL Server go slow when using variables?

Question

I have a sql query that runs super fast, around one second, when not using variables, like:

WHERE id BETWEEN 5461094 and 5461097

But when I

Answer 1

Actually, it was answered very well, I just write here a workaround as it worked for me:

Create a stored procedure with the SQL

WHERE id BETWEEN @firstId and @lastId

After then call the stored proc with parameters @firstId and @lastId and it will speed up. I still not 100% why it is working, but it works.