Why was the absence of Jane and Elizabeth from Longbourn welcomed by Mary Bennet?

The absence of Jane and Elizabeth allowed Mary to be appreciated for herself and not judged by the attributes or actions of her older sisters.

"Mary was the only daughter who remained at home; and she was necessarily drawn from the pursuit of accomplishments by Mrs. Bennet's being quite unable to sit alone. Mary was obliged to mix more with the world, but she could still moralize over every morning visit; and as she was no longer mortified by comparisons between her sisters' beauty and her own, it was suspected by her father that she submitted to the change without much reluctance."

Mary stays at home and keeps her mother company on her visits. THere is no longer competition and she grows out of her bookish ways. Mrs. Bennet, missing her other daughters, becomes closer with Marry.