2006 Toyota Seqouia battery will not charge after sitting up for 6 weeks

Most modern chargers have a feature where they will not put current into a battery that has too low of voltage. This is a safety feature to avoid cooking a bad battery which leads to bad things.

As Paulster2 mentioned in the comments a common way around this is to hook up another battery of the same voltage (12V for your car battery) in parallel (positive to positive, negative to negative) with the discharged battery. This will cause the charger to read a high enough voltage to start putting current into the battery. If the battery is just discharged without any other issues, it could charge it back up without a problem. Once the discharged battery's voltage is high enough, you can remove the second battery and charge normally.

Another solution is to get a charger with a manual mode that puts current into the battery regardless of the battery's voltage. Doing so on a low setting for an extended period of time can bring your battery back to life. However, because this charging mode isn't monitoring the batteries voltage you need to monitor the battery periodically to make sure it isn't overheating, spewing acid, etc.