INFORMATION_SCHEMA tables take so long when used in certain ways

Question

While attempting to find better ways to parse table schema data, the INFORMATION_SCHEMA articles were tested.

There must be way more going on behind the scenes then meets the eye. Using sys.* articles, being more verbose, are all reliably fast.

Can anyone explain why using the INFORMATION_SCHEMA articles produce a query plan the size of a Texas roadmap (see paste a plan)?

Also, the storing the output of INFORMATION_SCHEMA.TABLES into a #temp or @temp table reduces the query time from 8 minutes to 6 seconds when joined against INFORMATION_SCHEMA.TABLE_CONSTRAINTS and INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE.

Here is a paste the plan -> https://www.brentozar.com/pastetheplan/?id=SyRUqcEd6

The first query takes 2 seconds. The second query takes over 8 minutes.

DECLARE @X TABLE(TableName NVARCHAR(300))
INSERT INTO @X 
SELECT T.TABLE_NAME AS TableName FROM INFORMATION_SCHEMA.TABLES T 

----2 Seconds 740 Rows
SELECT 
    CU.COLUMN_NAME AS ColumnName,
    T.TableName AS TableName
FROM    
    @X T
    INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS CS ON CS.TABLE_NAME = T.TableName
    INNER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE CU ON CU.CONSTRAINT_NAME = CS.CONSTRAINT_NAME AND CS.CONSTRAINT_TYPE = 'PRIMARY KEY'  

GO

----8:47 Seconds 740 Rows
SELECT 
    CU.COLUMN_NAME AS ColumnName,
    T.TABLE_NAME AS TableName
FROM    
    INFORMATION_SCHEMA.TABLES T 
    INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS CS ON CS.TABLE_NAME = T.TABLE_NAME
    INNER JOIN INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE CU ON CU.CONSTRAINT_NAME = CS.CONSTRAINT_NAME AND CS.CONSTRAINT_TYPE = 'PRIMARY KEY'