I have read the book of acts and what you describe is true, the early christians gathered wherever they could to pray and worship. But that is not what is happening here.

Nothing could be clearer than the following verses:

Matthew 6:5 - 7

5. And when thou prayest, thou shalt not be as the hypocrites [are]: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward.

Jesus says you must definitely not pray as the hypocrites pray.

6 But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.
7 But when ye pray, use not vain repetitions, as the heathen [do]: for they think that they shall be heard for their much speaking.
Here Jesus says when thou prayest, you must pray this way:
(1) enter into thy closet.
(2) shut the door.
(3) pray to thy Father which is in secret.
(4) use not vain repetitions.

(Prayer must be in private, not in front of other people.
Do not repeat things over and over again in prayer)
An attribute of a true Christian is: He only prays in private, never in public